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Chapter 70 - Livestock Rearing

LIVESTOCK REARING: ITS EXTENT AND HEALTH EFFECTS

Melvin L. Myers

Overview

Humans depend upon animals for food and related by-products, work and a variety of other uses (see table 70.1). To meet these demands, they have domesticated or held in captivity species of mammals, birds, reptiles, fish and arthropods. These animals have become known as livestock, and rearing them has implications for occupational safety and health. This general profile of the industry includes its evolution and structure, the economic importance of different commodities of livestock, and regional characteristics of the industry and workforce. The articles in this chapter are organized by occupational processes, livestock sectors and consequences of livestock rearing.

Table 70.1 Livestock uses

Commodity

Food

By-products and other uses

Dairy

Fluid and dried milk, butter, cheese and curd,   casein, evaporated milk, cream, yoghurt and   other fermented milk, ice cream, whey

Male calves and old cows sold into the cattle commodity market; milk as an   industrial feedstock of carbohydrates (lactose as a diluent for drugs),   proteins (used as a surfactant to stabilize food emulsions) and fats (lipids   have potential uses as emulsifiers, surfactants and gels), offal

Cattle, buffalo, sheep

Meat (beef, mutton), edible tallow

Hides and skins (leather, collagens for sausage casings, cosmetics, wound   dressing, human tissue repair), offal, work (traction), wool, hair, dung (as   fuel and fertilizer), bone meal, religious objects, pet food, tallow and grease   (fatty acids, varnish, rubber goods, soaps, lamp oil, plastics, lubricants) fat,   blood meal

Poultry

Meat, eggs, duck eggs (in India)

Feathers and down, manure (as fertilizer), leather, fat, offal, flightless bird oil   (carrier for dermal path pharmaceuticals), weed control (geese in mint fields)

Pig

Meat

Hides and skins, hair, lard, manure, offal

Fish (aquaculture)

Meat

Fishmeal, oil, shell, aquarium pets

Horse, other equines

Meat, blood, milk

Recreation (riding, racing), work (riding, traction), glue, dog feed, hair

Micro-livestock (rabbit, guinea pig),   dog, cat

Meat

Pets, furs and skins, guard dogs, seeing-eye dogs, hunting dogs,   experimentation, sheep herding (by the dog), rodent control (by the cat)

Bulls

 

Recreation (bull-fighting, rodeo riding), semen

Insects and other invertebrates (e.g.,   vermiculture, apiculture)

Honey, 500 species (grubs, grasshoppers, ants,   crickets, termites, locusts, beetle larvae, wasps   and bees, moth caterpillars) are a regular diet   among many non-western societies

Beeswax, silk, predatory insects (>5,000 species are possible and 400 are   known as controls for crop pests; the carnivorous “tox” mosquito   (Toxorhynchites spp.) larvae feeds on the dengue fever vector,   vermicompositing, animal fodder, pollination, medicine (honeybee venom   to treat arthritis), scale insect products (shellac, red food dye, cochineal)

Sources: DeFoliart 1992; Gillespie 1997; FAO 1995; O’Toole 1995; Tannahil 1973;   USDA 1996a, 1996b.

Evolution and structure of the industry

Livestock evolved over the past 12,000 years through selection by human communities and adaptation to new environments. Historians believe that goat and sheep were the first species of animals domesticated for human use. Then, about 9,000 years ago, humans domesticated the pig. The cow was the last major food animal that humans domesticated, about 8,000 years ago in Turkey or Macedonia. It was probably only after cattle were domesticated that milk was discovered as a useful foodstuff. Goat, sheep, reindeer and camel milk were also used. People of the Indus valley domesticated the Indian jungle fowl primarily for its egg production, which became the world’s chicken, with its source of eggs and meat. People of Mexico had domesticated the turkey (Tannahill 1973).

Humans used several other mammalian and avian species for food, as well as amphibian and fish species and various arthropods. Insects have always provided an important source of protein, and today they are part of the human diet principally in the world’s non-western cultures (DeFoliart 1992). Honey from the honey bee was an early food; smoking bees from their nest to collect honey was known in Egypt as early as 5,000 years ago. Fishing is also an ancient occupation used to produce food, but because fishers are depleting wild fisheries, aquaculture has been the fastest growing contributor to fish production since the early 1980s, contributing about 14% to the total current production of fish (Platt 1995).

Humans also domesticated many mammals for use for draught, including the horse, donkey, elephant, dog, buffalo, camel and reindeer. The first animal used for draught, perhaps with the exception of the dog, was likely the goat, which could defoliate scrub for land cultivation through its browsing. Historians believe that Asians domesticated the Asian wolf, which was to become the dog, 13,000 years ago. The dog proved to be useful to the hunter for its speed, hearing and sense of smell, and the sheepdog aided in the early domestication of sheep (Tannahill 1973). The people of the steppe lands of Eurasia domesticated the horse about 4,000 years ago. Its use for work (traction) was stimulated by the invention of the horseshoe, collar harness and feeding of oats. Although draught is still important in much of the world, farmers displace draught animals with machines as farming and transportation becomes more mechanized. Some mammals, such as the cat, are used to control rodents (Caras 1996).

The structure of the current livestock industry can be defined by commodities, the animal products that enter the market. Table 70.2  shows a number of these commodities and the worldwide production or consumption of these products.

Table 70.2 International livestock production (1,000 tonnes)

Commodity

1991

1992

1993

1994

1995

1996

Beef and veal carcasses

  46,344

  45,396

  44,361

  45,572

  46,772

  47,404

Pork carcasses

  63,114

  64,738

  66,567

  70,115

  74,704

  76,836

Lamb, mutton, goat carcasses

    6,385

    6,245

    6,238

    6,281

    6,490

    6,956

Bovine hides and skins

    4,076

    3,983

    3,892

    3,751

    3,778

    3,811

Tallow and grease

    6,538

    6,677

    7,511

    7,572

    7,723

    7,995

Poultry meat

  35,639

  37,527

  39,710

  43,207

  44,450

  47,149

Cow’s milk

385,197

379,379

379,732

382,051

382,747

385,110

Shrimps

      815

      884

      N/A

      N/A

      N/A

      N/A

Molluscs

   3,075

   3,500

      N/A

      N/A

      N/A

      N/A

Salmonoids

      615

      628

      N/A

      N/A

      N/A

      N/A

Freshwater fish

   7,271

    7,981

      N/A

      N/A

      N/A

      N/A

Egg consumption (million pieces)

529,080

541,369

567,469

617,591

616,998

622,655

Sources: FAO 1995; USDA 1996a, 1996b.

Economic importance

The world’s growing population and increased per capita consumption both increased the global demand for meat and fish, the results of which are shown in figure 70.1 . Global meat production nearly trebled between 1960 and 1994. Over this period, per capita consumption increased from 21 to 33 kilograms per annum. Because of the limitations of available rangeland, beef production levelled off in 1990. As a result, animals that are more efficient in converting feed grain into meat, such as pigs and chickens, have gained a competitive advantage. Both pork and poultry have been increasing in dramatic contrast to beef production. Pork overtook beef in worldwide production in the late 1970s. Poultry may soon exceed beef production. Mutton production remains low and stagnant (USDA 1996a). Milk cows worldwide have been slowly decreasing while milk production has been increasing because of increasing production per cow (USDA 1996b).

Figure 70.1 World production of meat and fish

Sources: Brown 1995; Platt 1995.

Aquaculture production increased at an annual rate of 9.1% from 1984 to 1992. Aquaculture animal production increased from 14 million tonnes worldwide in 1991 to 16 million tonnes in 1992, with Asia providing 84% of world production (Platt 1995). Insects are rich in vitamins, minerals and energy, and provide between 5% and 10% of the animal protein for many people. They also become a vital source of protein during times of famine (DeFoliart 1992).

Regional Characteristics of the Industry and Workforce

Separating the workforce engaged in livestock rearing from other agricultural activities is difficult. Pastoral activities, such as those in much of Africa, and heavy commodity-based operations, such as those in the United States, have differentiated more between livestock and crop raising. However, many agro-pastoral and agronomic enterprises integrate the two. In much of the world, draught animals are still used extensively in crop production. Moreover, livestock and poultry depend upon feed and forage generated from crop operations, and these operations are commonly integrated. The principal aquaculture species in the world is the plant-eating carp. Insect production is also tied directly to crop production. The silkworm feeds exclusively on mulberry leaves; honeybees depend upon flower nectar; plants depend upon them for pollination work; and humans harvest edible grubs from various crops. The 1994 world population totalled 5,623,500,000, and 2,735,021,000 people (49% of the population) were engaged in agriculture (see figure 70.2). The largest contribution to this workforce is in Asia, where 85% of the agricultural population rear draught animals. Regional characteristics related to livestock rearing follow.

Figure 70.2 Human population engaged in agriculture by world region, 1994

Source: Scherf 1995.

Sub-Saharan Africa

Animal husbandry has been practised in sub-Saharan Africa for more than 5,000 years. Nomadic husbandry of the early livestock has evolved species that tolerate poor nutrition, infectious diseases and long migrations. About 65% of this region, much of it around desert areas, is suitable only for producing livestock. In 1994, 65% of the approximately 539 million people in sub-Saharan Africa depended upon agricultural income, down from 76% in 1975. Although its importance has grown since the mid-1980s, aquaculture has contributed little to the food supply for this region. Aquaculture in this region is based upon pond farming of tilapias, and export enterprises have attempted to culture marine shrimps. An export aquaculture industry in this region is expected to grow because Asian demand for fish is expected to increase, which will be fuelled by Asian investment and technology drawn to the region by a favourable climate and by African labour.

Asia and the Pacific

In Asia and the Pacific region, nearly 76% of the world’s agricultural population exists on 30% of the world’s arable land. About 85% of the farmers use cattle (bullocks) and buffaloes to cultivate and thresh crops.

Livestock rearing operations are mainly small-scale units in this region, but large commercial farms are establishing operations near urban centres. In rural areas, millions of people depend on livestock for meat, milk, eggs, hides and skins, draught power and wool. China exceeds the rest of the world with 400 million pigs; the remainder of the world has a total of 340 million pigs. India accounts for over one-fourth of the number of cattle and buffaloes worldwide, but because of religious policies that restrict cattle slaughter, India contributes less than 1% to the world’s beef supply. Milk production is a part of traditional agriculture in many countries of this region. Fish is a frequent ingredient in most people’s diet in this region. Asia contributes 84% of the world’s aquaculture production. At 6,856,000 tonnes, China alone produces nearly half of the world production,. Demand for fish is expected to increase rapidly, and aquaculture is expected to meet this demand.

Europe

In this region of 802 million people, 10.8% were engaged in agriculture in 1994, which has decreased significantly from 16.8% in 1975. Increased urbanization and mechanization have led to this decrease. Much of this arable land is in the moist, cool northern climates and is conducive to growing pastures for livestock. As a result, much of the livestock raising is located in the northern part of this region. Europe contributed 8.5% to the world’s production of aquaculture in 1992. Aquaculture has concentrated on relatively high-value species of finfish (288,500 tonnes) and shellfish (685,500 tonnes).

Latin America and the Caribbean

The Latin American and Caribbean region differs from other regions in many ways. Large tracts of land remain to be exploited, the region has large populations of domestic animals and much of the agriculture is operated as large operations. Livestock represents about one-third of the agricultural production, which makes up a significant part of the gross domestic product. Meat from beef cattle accounts for the largest share and makes up 20% of the world’s production. Most livestock species have been imported. Among those indigenous species that have been domesticated are guinea pigs, dogs, llamas, alpacas, Muscovy ducks, turkeys and black chickens. This region contributed only 2.3% to world aquaculture production in 1992.

Near East

Currently, 31% of the population of the Near East is engaged in agriculture. Because of the shortage of rainfall in this region, the only agricultural use for 62% of this land area is animal grazing. Most of the major livestock species were domesticated in this region (goats, sheep, pigs and cattle) at the confluence of the Tigris and Euphrates rivers. Later, in North Africa, water buffaloes, dromedary camels and asses were domesticated. Some livestock raising systems that existed in ancient times still exist today. These are subsistence systems in Arab tribal society, in which herds and flocks are moved seasonally over great distances in search of feed and water. Intensive farming systems are used in the more developed countries.

North America

Although agriculture is a major economic activity in Canada and the United States, the proportion of the population engaged in agriculture is less than 2.5%. Since the 1950s, agriculture has become more intensive, leading to fewer but larger farms. Livestock and livestock products make up a major proportion of the population’s diet, contributing 40% to the total food energy. The livestock industry in this region has been very dynamic. Introduced animals have been bred with indigenous animals to form new breeds. Consumer demand for leaner meats and eggs with less cholesterol is having an impact on breeding policy. Horses were used extensively at the turn of the nineteenth century, but they have declined in numbers because of mechanization. They are currently used in the race horse industry or for recreation. The United States has imported about 700 insect species to control more than 50 pests. Aquaculture in this region is growing, and accounted for 3.7% of the world’s aquaculture production in 1992 (FAO 1995; Scherf 1995).

Environmental and Public Health Issues

Occupational hazards of livestock rearing may lead to injuries, asthma or zoonotic infections. In addition, livestock rearing poses several environmental and public health issues. One issue is the effect of animal waste upon the environment. Other issues include the loss of biological diversity, risks associated with animal and product importation and food safety.

Water and air pollution

Animal wastes pose potential environmental consequences of water and air pollution. Based upon US annual discharge factors shown in table 70.3 , major livestock breeds discharged a total of 14.3 billion tonnes of faeces and urine worldwide in 1994. Of this total, cattle (milk and beef) discharged 87%; pigs, 9%; and chickens and turkeys, 3% (Meadows 1995). Because of their high annual discharge factor of 9.76 tonnes of faeces and urine per animal, cattle contributed the most waste among these livestock types for all six United Nations Food and Agricultural Organization (FAO) regions of the world, ranging from 82% in both Europe and Asia to 96% in sub-Saharan Africa.

Table 70.3 Annual US livestock faeces and urine production

Livestock type

Population

Waste (tonnes)

Tonnes per animal

Cattle (milk and beef)

     46,500,000

450,000,000

   9.76

Pig

     60,000,000

  91,000,000

   1.51

Chicken and turkey

7,500,000,000

270,000,000

   0.04

Source: Meadows 1995.

In the United States, farmers who specialize in livestock rearing do not engage in crop farming, as had been the historical practice. As a result, livestock waste is no longer systematically applied to crop land as a fertilizer. Another problem with modern livestock raising is the high concentration of animals into small areas such as confinement buildings or feedlots. Large operations may confine 50,000 to 100,000 cattle, 10,000 pigs or 400,000 chickens to an area. In addition, these operations tend to cluster near the processing plants to shorten the transportation distance of the animals to the plants.

Several environmental problems result from concentrated operations. These problems include lagoon spills, chronic seepage and runoff and airborne health effects. Nitrate peculation into the groundwater and runoff from fields and feedlots are major contributors to water contamination. A greater use of feedlots leads to concentration of animal manure and a greater risk for contamination of groundwater. Waste from cattle and pig operations is typically collected in lagoons, which are large, shallow pits dug into the ground. Lagoon design depends upon the settling of solids to the bottom, where they anaerobically digest, and the excess liquids are controlled by spraying them onto nearby fields before they overflow (Meadows 1995).

Biodegrading livestock waste also emits odorous gases that contain as many as 60 compounds. These compounds include ammonia and amines, sulphides, volatile fatty acids, alcohols, aldehydes, mercaptans, esters and carbonyls (Sweeten 1995). When humans sense odours from concentrated livestock operations, they can experience nausea, headaches, breathing problems, sleep interruption, appetite loss and irritation of the eyes, ears and throat.

Less understood are the adverse effects of livestock waste upon global warming and atmospheric deposition. Its contribution to global warming is through the generation of the greenhouse gases, carbon dioxide and methane. Livestock manure may contribute to nitrogen depositions because of ammonia release from waste lagoons into the atmosphere. Atmospheric nitrogen re-enters the hydrologic cycle through rain and flows into streams, rivers, lakes and coastal waters. Nitrogen in water contributes to increased algae blooms that reduce the oxygen available to fish.

Two modifications in livestock production offer solutions to some of the problems of pollution. These are less animal confinement and improved waste treatment systems.

Animal diversity

The potential for rapid loss of genes, species and habitats threatens the adaptability and traits of a variety of animals that are or could be useful. International efforts have stressed the need to preserve biological diversity at three levels: genetic, species and habitat. An example of declining genetic diversity is the limited number of sires used to breed artificially females of many livestock species (Scherf 1995).

With the decline of many livestock breeds, and thus the reduction of species diversity, dominant breeds have been increasing, with an emphasis on uniformity in higher production breeds. The problem of a lack of dairy cattle-breed diversity is particularly acute; with the exception of the high-producing Holstein, dairy populations are declining. Aquaculture has not reduced pressure on wild fish populations. For example, the use of fine nets for biomass fishing for shrimp food results in the collection of juveniles of valuable wild species, which adds to their depletion. Some species, such as groupers, milkfish and eels, cannot be bred in captivity, so their juveniles are caught in the wild and raised on fish farms, further reducing the stock of wild populations.

An example of a loss of habitat diversity is the impact of feed for fish farms on wild populations. Fish feed used in coastal areas affects wild populations of shrimp and fish by destroying their natural habitat such as mangroves. In addition, fish faeces and feed can accumulate on the bottom and kill the benthic communities that filter the water (Safina 1995).

Animal species that survive in abundance are those used as a means to human ends, but a social dilemma emerges from an animal rights movement that espouses that animals, especially warm-blooded animals, are not to be used as a means to human ends. Preceding the animal rights movement, an animal welfare movement started before the mid-1970s. Animal welfare proponents advocate the humane treatment of animals that are used for research, food, clothing, sport or companionship. Since the mid-1970s, the animal rights advocates assert that sentient animals have a right not to be used for research. It appears highly unlikely that the human use of animals will be abolished. It is also likely that animal welfare will continue as a popular movement (NIH 1988).

Animal and animal product importation

The history of livestock rearing is closely linked to the history of livestock importation into new areas of the world. Diseases spread with the spread of imported livestock and their products. Animals may carry disease that can infect other animals or humans, and countries have established quarantine services to control the spread of these zoonotic diseases. Among these diseases are scrapie, brucellosis, Q-fever and anthrax. Livestock and food inspection and quarantines have emerged as methods to control disease importation (MacDiarmid 1993).

Public concern about the potential infection of humans with the rare Creutzfeldt-Jakob disease (CJD) emerged among beef-importing nations in 1996. Eating beef infected with bovine spongiform encephalopathy (BSE), popularly known as mad cow disease, is suspected of leading to CJD infection. Although unproven, public perceptions include the proposition that the disease may have entered cattle from feed containing bone meal and offal from sheep afflicted with the similar disease, scrapie. All three diseases, in humans, cattle and sheep, exhibit common symptoms of sponge-like brain lesions. The diseases are fatal, their causes are unknown, and there are no tests to detect them. Britons launched a pre-emptive slaughter of one-third of their cattle population in 1996 to control BSE and restore consumer confidence in the safety of their beef exports (Aldhous 1996).

The importation of African bees into Brazil has also emerged into a public health issue. In the United States, subspecies of European bees produce honey and beeswax and pollinate crops. They rarely swarm aggressively, which aids safe beekeeping. The African subspecies has migrated from Brazil into Central America, Mexico and the Southeastern United States. This bee is aggressive and will swarm in defence of its colony. It has interbred with the European subspecies, which results in an Africanized bee that is more aggressive. The public health threat is multiple stings when the Africanized bee swarms and severe toxic reactions in humans.

Two controls currently exist for the Africanized bee. One is that they are not hardy in northern climates and may be restricted to warmer temperate climates like the Southern United States. The other control is routinely to replace the queen bee in hives with queen bees of the European subspecies, although this does not control wild colonies (Schumacher and Egen 1995).

Food safety

Many human food-borne illnesses result from pathogenic bacteria of animal origin. Examples include listeria and salmonellae found in dairy products and salmonellae and campylobacter found in meat and poultry. The Centers for Disease Control and Prevention estimates that 53% of all food-borne illness outbreaks in the United States were caused by bacterial contamination of animal products. They estimate that 33 million food-borne illnesses occur each year, from which 9,000 deaths result.

The subtherapeutic feeding of antibiotics and antibiotic treatment of diseased animals are current animal health practices. The potential diminished effectiveness of antibiotics for disease therapy is a rising concern because of the frequent development of antibiotic resistance of zoonotic pathogens. Many antibiotics added to animal feed are also used in human medicine, and antibiotic-resistant bacteria could develop and cause infections in animals and humans.

Drug residues in food that result from medication of livestock also present risks. Residues of antibiotics used in livestock or added to feed have been found in food-producing animals including dairy cows. Among these drugs are chloramphenicol and sulphamethazine. Alternatives to the prophylactic feeding use of antibiotics to maintain animal health include the modification of production systems. These modifications include reduced animal confinement, improved ventilation and improved waste treatment systems.

Diet has been associated with chronic diseases. Evidence of an association between fat consumption and heart disease has stimulated efforts to produce animal products with less fat content. These efforts include animal breeding, feeding intact rather than castrated males and genetic engineering. Hormones are also seen as a method for decreasing fat content in meat. Porcine growth hormones increase growth rate, feed efficiency and the ratio of muscle to fat. The growing popularity of low-fat, low-cholesterol species such as ostriches is another solution (NRC 1989).

HEALTH PROBLEMS AND DISEASE PATTERNS

Kendall Thu, Craig Zwerling and Kelley Donham

The domestication of animals occurred independently in a number of areas of the Old and New World over 10,000 years ago. Until domestication, hunting and gathering was the predominant subsistence pattern. The transformation to human control over animal and plant production and reproduction processes resulted in revolutionary changes in the structure of human societies and their relationships to the environment. The change to agriculture marked an increase in labour intensity and work time spent in food procurement-related activities. Small nuclear families, adapted to nomadic hunting and gathering groups, were transformed into large, extended, sedentary social units suited to labour-intensive domesticated food production.

The domestication of animals increased human susceptibility to animal-related injuries and diseases. Larger non-nomadic populations quartered in close proximity to animals provided greater opportunity for transmission of disease between animals and humans. The development of larger herds of more intensely handled livestock also increased the likelihood of injuries. Throughout the world, differing forms of animal agriculture are associated with varying risks for injury and disease. For example, the 50 million inhabitants who practice swidden (cut and burn) agriculture in equatorial regions face different problems from the 35 million pastoral nomads across Scandinavia and through central Asia or the 48 million food producers who practise an industrialized form of agriculture.

In this article, we provide an overview of selected injury patterns, infectious diseases, respiratory diseases and skin diseases associated with livestock production. The treatment is topically and geographically uneven because most research has been conducted in industrialized countries, where intensive forms of livestock production are common.

Overview

Types of human health problems and disease patterns associated with livestock production can be grouped according to the type of contact between animals and people (see table 70.4). Contact can occur via direct physical interaction, or contact with an organic or inorganic agent. Health problems associated with all types of livestock production can be grouped into each of these areas.

Table 70.4 Types of human health problems associated with livestock production

Health problems from direct physical contact

  • Allergic contact dermatitis
  • Allergic rhinitis
  • Bites, kicks, crushing
  • Envenomation and possible hypersensitivity
  • Asthma
  • Scratches
  • Traumatic injury

Health problems from organic agents

  • Agrochemical poisoning
  • Antibiotic resistance
  • Chronic bronchitis
  • Contact dermatitis
  • Allergies from drug residue food exposures
  • Food-borne illnesses
  • "Farmer’s lung"
  • Hypersensitivity pneumonitis
  • Mucous membrane irritation
  • Occupational asthma
  • Organic dust toxic syndrome (ODTS)
  • Allergies from pharmaceutical exposures
  • Zoonotic diseases

Health problems from physical agents

  • Hearing loss
  • Machinery-related trauma
  • Methane emission and greenhouse effect
  • Musculoskeletal disorders
  • Stress

Direct human contact with livestock ranges from the brute force of large animals such as the Chinese buffalo to the undetected skin contact by microscopic hairs of the Japanese oriental tussock moth. A corresponding range of health problems can result, from the temporary irritant to the debilitating physical blow. Notable problems include traumatic injuries from handling large livestock, venom hypersensitivity or toxicosis from venomous arthropod bites and stings, and contact and allergic contact skin dermatitis.

A number of organic agents utilize various pathways from livestock to humans, resulting in a range of health problems. Among the most globally important are zoonotic diseases. Over 150 zoonotic diseases have been identified worldwide, with approximately 40 significant for human health (Donham 1985). The importance of zoonotic diseases depends on regional factors such as agricultural practices, environment and a region’s social and economic status. The health consequences of zoonotic diseases range from the relatively benign flu-like symptoms of brucellosis to debilitating tuberculosis or potentially lethal strains of Escherichia coli or rabies.

Other organic agents include those associated with respiratory disease. Intensive livestock production systems in confined buildings create enclosed environments where dust, including microbes and their by-products, becomes concentrated and aerosolized along with gases that are in turned breathed by people. Approximately 33% of swine confinement workers in the United States suffer from organic dust toxic syndrome (ODTS) (Thorne et al. 1996).

Comparable problems exist in dairy barns, where dust containing endotoxin and/or other biologically active agents in the environment contributes to bronchitis, occupational asthma and inflammation of the mucous membrane. While these problems are most notable in developed countries where industrialized agriculture is widespread, the increasing export of confined livestock production technologies to developing areas such as Southeast Asia and Central America increases the risks for workers there.

Health problems from physical agents typically involve tools or machinery either directly or indirectly involved with livestock production in the agricultural work environment. Tractors are the leading cause of farm fatalities in developed countries. In addition, elevated rates of hearing loss associated with machinery and confined livestock production noises, and musculoskeletal disorders from repetitive motions, are also consequences of industrialized forms of animal agriculture. Agricultural industrialization, characterized by the use of capital-intensive technologies which interface between humans and the physical environment to produce food, is behind the growth of physical agents as significant livestock-related health factors.

Injuries

Direct contact with livestock is a leading cause of injuries in many industrialized regions of the world. In the United States, the national Traumatic Injury Surveillance of Farmers (NIOSH 1993) indicates that livestock is the primary source of injury, with cattle, swine and sheep constituting 18% of all agricultural injuries and accounting for the highest rate of lost workdays. This is consistent with a 1980-81 survey conducted by the US National Safety Council (National Safety Council 1982).

Regional US studies consistently show livestock as a leading cause of injury in agricultural work. Early work on hospital visits by farmers in New York from 1929 to 1948 revealed livestock accounting for 17% of farm-related injuries, second only to machinery (Calandruccio and Powers 1949). Such trends continue, as research indicates livestock account for at least one-third of agricultural injuries among Vermont dairy farmers (Waller 1992), 19% of injuries among a random sample of Alabama farmers (Zhou and Roseman 1995), and 24% of injuries among Iowa farmers (Iowa Department of Public Health 1995). One of the few studies to analyse risk factors for livestock-specific injuries indicates such injuries may be related to the organization of production and specific features of the livestock rearing environment (Layde et al. 1996).

Evidence from other industrialized agricultural areas of the world reveals similar patterns. Research from Australia indicates that livestock workers have the second-highest occupational fatal injury rates in the country (Erlich et al. 1993). A study of accident records and emergency department visits of British farmers in West Wales (Cameron and Bishop 1992) reveals livestock were the leading source of injuries, accounting for 35% of farm-related accidents. In Denmark, a study of 257 hospital-treated agricultural injuries revealed livestock as the second-leading cause of injuries, accounting for 36% of injuries treated (Carstensen, Lauritsen and Rasmussen 1995). Surveillance research is necessary to address the lack of systematic data on livestock-related injury rates in developing areas of the world.

Prevention of livestock-related injuries involves understanding animal behaviour and respecting dangers by acting appropriately and using appropriate control technologies. Understanding animal habits related to feeding behaviours and environmental fluctuations, social relationships such as animals isolated from their herd, nurturing and protective instincts of female animals and the variable territorial nature and feeding patterns of livestock are critical in reducing the risk of injury. Prevention of injury also depends on using and maintaining livestock control equipment such as fences, pens, stalls and cages. Children are at particular risk and should be supervised in designated play areas well away from livestock holding areas.

Infectious Diseases

Zoonotic diseases can be classified according to their modes of transmission, which are in turn linked to forms of agriculture, human social organization and the ecosystem. The four general routes of transmission are:

1.     direct single vertebrate host

2.     cyclical multiple vertebrate host

3.     combination vertebrate-invertebrate host

4.     inanimate intermediary host.

Zoonotic diseases can be generally characterized as follows: they are non-fatal, infrequently diagnosed and sporadic rather than epidemic; they mimic other diseases; and humans are typically the dead-end hosts. Primary zoonotic diseases by region are listed in table 70.5 .

Table 70.5 Primary zoonoses by world region

Common name

Principal source

Region

Anthrax

Mammals

Eastern Mediterranean, West and Southeast Asia, Latin America

Brucellosis

Goats, sheep, cattle, swine

Europe, Mediterranean area, United States

Encephalitis, arthropod-borne

Birds, sheep, rodents

Africa, Australia, Central Europe, Far East, Latin America, Russia, United States

Hydatidosis

Dogs, ruminants, swine, wild carnivores

Eastern Mediterranean, southern South America, South and East Africa,   New Zealand, southern Australia, Siberia

Leptospirosis

Rodents, cattle, swine, wild carnivores, horses

Worldwide, more prevalent in Caribbean

Q fever

Cattle, goats, sheep

Worldwide

Rabies

Dogs, cats, wild carnivores, bats

Worldwide

Salmonellosis

Birds, mammals

Worldwide, most prevalent in regions with industrial agriculture and higher use   of antibiotics

Trichinosis

Swine, wild carnivores, Arctic animals

Argentina, Brazil, Central Europe, Chile North America, Spain

Tuberculosis

Cattle, dogs, goats

Worldwide, most prevalent in developing countries

Rates of zoonotic diseases among human populations are largely unknown owing to the lack of epidemiological data and to misdiagnoses. Even in industrialized countries such as the United States, zoonotic diseases such as leptospirosis are frequently mistaken for influenza. Symptoms are non-specific, making diagnosis difficult, a characteristic of many zoonoses.

Prevention of zoonotic diseases consists of a combination of disease eradication, animal vaccinations, human vaccinations, work environment sanitation, cleaning and protecting open wounds, appropriate food handling and preparation techniques (such as pasteurization of milk and thorough cooking of meat), use of personal protection equipment (such as boots in rice fields) and prudent use of antibiotics to reduce the growth of resistant strains. Control technologies and preventive behaviours should be conceptualized in terms of pathways, agents and hosts and specifically targeted to the four routes of transmission.

Respiratory Diseases

Given the variety and extent of exposures related to livestock production, respiratory diseases may be the major health problem. Studies in some sectors of livestock production in developed areas of the world reveal that 25% of livestock workers suffer from some form of respiratory disease (Thorne et al. 1996). The kinds of work most commonly associated with respiratory problems include grain production and handling and working in animal confinement units and dairy farming.

Agricultural respiratory diseases may result from exposures to a variety of dusts, gases, agricultural chemicals and infectious agents. Dust exposures may be divided into those primarily consisting of organic components and those consisting mainly of inorganic components. Field dust is the primary source of inorganic dust exposures. Organic dust is the major respiratory exposure to agricultural production workers. Disease results from periodic short-term exposures to agricultural organic dust containing large numbers of microbes.

ODTS is the acute flu-like illness seen following periodic short-term exposure to high concentrations of dust (Donham 1986). This syndrome has features very similar to those of acute farmer’s lung, but does not carry the risk of pulmonary impairment associated with farmer’s lung. Bronchitis affecting agricultural workers has both an acute and chronic form (Rylander 1994). Asthma, as defined by reversible airway obstruction associated with airway inflammation, can also be caused by agricultural exposures. In most cases this type of asthma is related to chronic inflammation of the airways rather than a specific allergy.

A second common exposure pattern is daily exposure to a lower level of organic dust. Typically, total dust levels are 2 to 9 mg/m3, microbe counts are at 103 to 105 organisms/m3 and endotoxin concentration is 50 to 900 EU/m3. Examples of such exposures include work in a swine confinement unit, a dairy barn or a poultry-growing facility. Usual symptoms seen with these exposures include those of acute and chronic bronchitis, an asthma-like syndrome and symptoms of mucous membrane irritation.

Gases play an important role in causing lung disorders in the agricultural setting. In swine confinement buildings and in poultry facilities, ammonia levels often contribute to respiratory problems. Exposure to the fertilizer anhydrous ammonia has both acute and long-term effects on the respiratory tract. Acute poisoning from hydrogen sulphide gas released from manure storage facilities in dairy barns and swine confinement units can cause fatalities. Inhalation of insecticidal fumigants can also lead to death.

Prevention of respiratory illnesses may be aided by controlling the source of dusts and other agents. In livestock buildings, this includes managing a correctly designed ventilation system and frequent cleaning to prevent build-up of dust. However, engineering controls alone are likely insufficient. Correct selection and use of a dust respirator is also needed. Alternatives to confinement operations can also be considered, including pasture-based and partially enclosed production arrangements, which can be as profitable as confined operations, particularly when occupational health costs are considered.

Skin Problems

Skin problems can be categorized as contact dermatitis, sun-related, infectious or insect-induced. Estimates indicate that agricultural workers are at highest occupational risk for certain dermatoses (Mathias 1989). While prevalence rates are lacking, particularly in developing regions, studies in the United States indicate that occupational skin disease may account for up to 70% of all occupational diseases among agricultural workers in certain regions (Hogan and Lane 1986).

There are three types of contact dermatoses: irritant dermatitis, allergic dermatitis and photocontact dermatitis. The most common form is irritant contact dermatitis, while allergic contact dermatitis is less common and photocontact reactions are rare (Zuehlke, Mutel and Donham 1980). Common sources of contact dermatitis on the farm include fertilizers, plants and pesticides. Of particular note is dermatitis from contact with livestock feed. Feeds containing additives such as antibiotics may result in allergic dermatitis.

Light-complexioned farmers in developing areas of the world are at particular risk for chronic sun-induced skin problems, including wrinkling, actinic keratoses (scaly non-cancerous lesions) and skin cancer. The two most common types of skin cancer are squamous and basal cell carcinomas. Epidemiological work in Canada indicates that farmers are at higher risk for squamous cell carcinoma than non-farmers (Hogan and Lane 1986). Squamous cell carcinomas often arise from actinic keratoses. Approximately 2 out of 100 squamous cell carcinomas metastasize, and they are most common on the lips. Basal cell carcinomas are more common and occur on the face and ears. While locally destructive, basal cell carcinomas rarely metastasize. 

Infectious dermatoses most relevant for livestock workers are ringworm (dermatophytic fungi), orf (contagious ecthyma) and milker’s nodule. Ringworm infections are superficial skin infections that appear as red scaling lesions that result from contact with infected livestock, particularly dairy cattle. A study from India, where cattle generally roam free, revealed over 5% of rural inhabitants suffering from ringworm infections (Chaterjee et al. 1980). Orf, by contrast, is a pox virus usually contracted from infected sheep or goats. The result is typically lesions on the backs of hands or fingers which usually disappear with some scarring in about 6 weeks. Milker’s nodules result from infection with the pseudocowpox poxvirus, typically from contact with infected udders or teats of milk cows. These lesions appear similar to those of orf, though they are more often multiple.

Insect-induced dermatoses result primarily from bites and stings. Infections from mites that parasitize livestock or contaminate grains is particularly notable among livestock handlers. Chigger bites and scabies are typical skin problems from mites that result in various forms of reddened irritations that usually heal spontaneously. More serious are bites and stings from various insects such as bees, wasps, hornets or ants that result in anaphylactic reactions. Anaphylactic shock is a rare hypersensitivity reaction that occurs with an overproduction of chemicals emitted from white blood cells that result in constriction of the airways and can lead to cardiac arrest.

All of these skin problems are largely preventable. Contact dermatitis can be prevented by reducing exposures through use of protective clothing, gloves and appropriate personal hygiene. Additionally, insect-related problems can be prevented by wearing light-coloured and nonflowery clothing and by avoiding scented skin applications. The risk of skin cancer can be dramatically reduced by using appropriate clothing to minimize exposure, such as a wide-brimmed hat. Use of appropriate sunscreen lotions can also be helpful, but should not be relied upon.

Conclusion

The number of livestock worldwide has grown apace with the increase in human population. There are approximately 4 billion cattle, pigs, sheep, goats, horses, buffalo and camels in the world (Durning and Brough 1992). However, there is a notable lack of data on livestock-related human health problems in developing areas of the world such as China and India, where much of the livestock currently reside and where future growth is likely to occur. However, given the emergence of industrialized agriculture worldwide, it can be anticipated that many of the health problems documented in North American and European livestock production will likely accompany the emergence of industrialized livestock production elsewhere. It is also anticipated that health services in these areas will be inadequate to deal with the health and safety consequences of industrialized livestock production generally described here.

The worldwide emergence of industrialized livestock production with its attendant human health consequences will accompany fundamental changes in the social, economic and political order comparable to those that followed from the domestication of animals over 10,000 years ago. Preventing human health problems will require broad understanding and appropriate engagement of these new forms of human adaptation and the place of livestock production within them.

ARTHROPOD-RELATED OCCUPATIONAL HEALTH PROBLEMS

Arthropods comprise more than 1 million species of insects and thousands of species of ticks, mites, spiders, scorpions and centipedes. Bees, ants, wasps and scorpions sting and inject venom; mosquitoes and ticks suck blood and transmit diseases; and the scales and hairs from insect bodies can irritate the eyes and skin, as well as tissues in the nose, mouth and respiratory system. Most stings in humans are from social bees (bumble bees, honey bees). Other stings are from paper wasps, yellow jackets, hornets and ants.

Arthropods can be a health hazard in the workplace (see table 70.6), but in most cases, potential arthropod hazards are not unique to specific occupations. Rather, exposure to arthropods in the workplace depends on geographic location, local conditions and the time of year. Table 70.7 lists some of these hazards and their corresponding arthropod agents. For all arthropod hazards, the first line of defence is avoidance or exclusion of the offending agent. Venom immunotherapy may increase a persons's tolerance to arthropod venom and is accomplished by injecting increasing doses of venom over time. It is effective in 90 to 100% of cenom hypersensitive individuals but involves an indefinite course of expensive injections. Table 70.8  lists normal and allergic reactions to insect stings.

Donald Barnard

Table 70.6 Different occupations and their potential for contact with arthropods that may adversely affect health and safety.

Occupation

Arthropods

Construction personnel, environmentalists, farmers, fishers, foresters, fish and wildlife workers, naturalists, transportation workers, park rangers, utility workers

Ants, bees, biting flies, caterpillars, chiggers, centipedes, caddisflies, fly maggots, mayflies, scorpions, spiders, ticks, wasps

Cosmetics manufacturers, dock workers, dye makers, factory workers, food processors, grainery workers, homemakers, millers, restaurant workers

Ants; beetles; bean, grain and pea weevils; mites; scale insects; spiders

Beekeepers

Ants, bumble bees, honey bees, wasps

Insect production workers, laboratory and field biologists, museum curators

Over 500 species of arthropods are reared in the laboratory. Ants, beetles, mites, moths, spiders and ticks are especially important.

Hospital and other health care workers, school administrators, teachers

Ants, beetles, biting flies, caterpillars, cockroaches, mites

Silk producers

Silk worms

Table 70.7 Potential arthropod hazards in the workplace and their causative agent(s)

Hazard

Arthropod agents

Bites, envenomation1

Ants, biting flies, centipedes, mites, spiders

Sting envenomation, venom hypersensitivity2

Ants, bees, wasps, scorpions

Tick toxicosis/paralysis

Ticks

Asthma

Beetles, caddisflies, caterpillars, cockroaches, crickets, dust mites, fly maggots, grain mites, grain weevils, grasshoppers, honeybees, mayflies, moths, silk worms

Contact dermatitis3

Blister beetles, caterpillars, cockroaches, dried fruit mites, dust mites, grain mites, straw itch mites, moths, silk worms, spiders

1 Envenomation with poison from glands associated with mouthparts.

2 Envenomation with poison from glands not associated with mouthparts.

3 Includes primary irritant and allergic dermatitis.

Table 70.8 Normal and allergic reactions to insect sting

Type of response

Reaction

I. Normal, non-allergic reactions at the time of the sting

Pain, burning, itching, redness at the sting site, white area surrounding the sting site, swelling, tenderness

II. Normal, non-allergic reactions hours or days after sting

Itching, residual redness, small brown or red damage spot at sting site, swelling at the sting site

III. Large local reactions

Massive swelling around the sting site extending over an area 10 cm or more and increasing in size for 24 to 72 hours, sometimes lasting up to a week or more

IV. Cutaneous allergic reactions

Hives anywhere on the skin, massive swelling remote from the sting site, generalized itching of the skin, generalized redness of the skin remote from the sting site

V. Non life-threatening systemic allergic reactions

Allergic rhinitis, minor respiratory symptoms, abdominal cramps

VI. Life-threatening systemic allergic reactions

Shock, unconsciousness, hypotension or fainting, difficulty in breathing, massive swelling in the throat.

Source: Schmidt 1992.

FORAGE CROPS

Lorann Stallones

As populations tended to concentrate and the need for winter feeding in northern climates grew, the need to harvest, cure and feed hay to domestic animals emerged. Although pasture dates to the earliest domestication of animals, the first cultivated forage plant may have been alfalfa, with its recorded use dating back to 490 BC in Persia and Greece.

Livestock forage is a crucial input for livestock rearing. Forages are grown for their vegetation and not their grains or seeds. Stems, leaves and inflorescences (flower clusters) of some legumes (e.g., alfalfa and clover) and a variety of non-legume grasses are used for grazing or harvested and fed to livestock. When grain crops such as corn, sorghum or straw are harvested for their vegetation, they are considered forage crops.

Production Processes

The major categories of forage crops are pastures and open ranges, hay and silage. Forage crops can be harvested by livestock (in pastures) or by humans, either by hand or machinery. The crop can be used for farm feeding or for sale. In forage production, tractors are a source of traction and processing power, and, in dry areas, irrigation may be required.

Pasture is fed by allowing the livestock to graze or browse. The type of pasture crop, typically grass, varies in its production with the season of the year, and pastures are managed for spring, summer and fall grazing. Range management focuses on not overgrazing an area, which involves rotating livestock from one area to another. Crop residues may be part of the pasture diet for livestock.

Alfalfa, a popular hay crop, is not a good pasture crop because it causes bloating in ruminants, a condition of a gas build-up in the rumen (the first part of the cow’s stomach) that can kill a cow. In temperate climates, pastures are ineffective as a feed source in the winter, so stored feed is needed. Moreover, in large operations, harvested forage—hay and silage—is used because pasture is impractical for large concentrations of animals.

Hay is forage that is grown and dry-cured before storage and feeding. After the hay crop has grown, it is cut with a mowing machine or swather (a machine that combines the mowing and raking operations) and raked by a machine into a long row for drying (a windrow). During these two processes it is field cured for baling. Historically harvesting was done by pitchforking loose hay, which may still be used to feed the animals. Once cured, the hay is baled. The baling machine picks up the hay from the windrow, and compresses and wraps it into either a small square bale for manual handling, or large square or round bales for mechanical handling. The small bale may be kicked mechanically from the baler back into a trailer, or it may be picked up by hand and placed—a task called bucking—onto a trailer for transport to the storage area. The bales are stored in stacks, usually under a cover (barn, shed or plastic) to protect them from rain. Wet hay can easily spoil or spontaneously combust from the heat of the decaying process. Hay may be processed for commercial use into compressed pellets or cubes. A crop can be cut several times in a season, three times being typical. When it is fed, a bale is moved to the feeding trough, opened and placed into the trough where the animal can reach it. This part of the operation is typically manual.

Other forage that is harvested for livestock feeding is corn or sorghum for silage. The economic advantage is that corn has as much as 50% more energy when harvested as silage than grain. A machine is used to harvest most of the green plant. The crop is cut, crushed, chopped and ejected into a trailer. The material is then fed as green chop or stored in a silo, where it undergoes fermentation in the first 2 weeks. The fermentation establishes an environment that prevents spoilage. Over a year, the silo is emptied as the silage is fed to livestock. This feeding process is primarily mechanical.

Hazards and Their Prevention

The storage of animal feed presents health hazards for workers. Early in the storage process, nitrogen dioxide is produced and can cause serious respiratory damage and death (“silo filler’s disease”). Storage in enclosed environments, such as silos, can create this hazard, which can be avoided by not entering silos or enclosed storage spaces in the first few weeks after feed has been stored. Further problems can occur later if the alfalfa, hay, straw or other forage crop was wet when it was stored and there is a build-up of fungi and other microbial contaminants. This can result in acute respiratory illness (“silo unloader’s disease”, organic dust toxicity) and/or chronic respiratory diseases (“farmer’s lung”). The risk of acute and chronic respiratory diseases can be reduced through the use of appropriate respirators. There should also be appropriate confined space entry procedures.

The straw and hay used for bedding is usually dry and old, but may contain moulds and spores which can cause respiratory symptoms when dust is made airborne. Dust respirators can reduce exposure to this hazard.

Harvesting and baling equipment and bedding choppers are designed to chop, cut and mangle. They have been associated with traumatic injuries to farm workers. Many of these injuries occur when workers try to clear clogged parts while the equipment is still operating. The equipment should be turned off before clearing jams. If more than one person is working, then a lockout/tagout programme should be in effect. Another major source of injuries and fatalities is tractor overturns without proper roll-over protection for the driver (Deere & Co. 1994). More information on farm machinery hazards is also discussed elsewhere in this Encyclopaedia.

Where animals are used to plant, harvest and store feed, there is a possibility of animal-related injuries from kicks, bites, strains, sprains, crush injuries and lacerations. Correct animal handling techniques are the most likely means to reduce these injuries.

Manual handling of bales of hay and straw can result in ergonomic problems. Workers should be trained in correct lifting procedures, and mechanical equipment should be used where possible.

Forage and bedding are fire hazards. Wet hay, as mentioned previously, is a spontaneous combustion hazard. Dry hay, straw and so forth will burn easily, especially when loose. Even bailed forage is a major fuel source in a fire. Basic fire precautions should be instituted, such as no-smoking rules, elimination of spark sources and fire suppression measures.

LIVESTOCK CONFINEMENT

Kelley Donham

Global economic forces have contributed to the industrialization of agriculture (Donham and Thu 1995). In the developed countries, there are trends toward increased specialization, intensity and mechanization. Increased confinement production of livestock has been a result of these trends. Many developing countries have recognized the need to adopt confinement production in an attempt to transform their agriculture from a subsistence to a globally competitive enterprise. As more corporate organizations obtain ownership and control of the industry, fewer, but larger, farms with many employees replace the family farm.

Conceptually, the confinement system applies principles of industrial mass production to livestock production. The concept of confinement production includes raising animals in high densities in structures that are isolated from the outside environment and equipped with mechanical or automated systems for ventilation, waste handling, feeding and watering (Donham, Rubino et al. 1977).

Several European countries have been using confinement systems since the early 1950s. Livestock confinement started to appear in the United States in the late 1950s. Poultry producers were first to use the system. By the early 1960s, the swine industry had also started to adopt this technique, followed more recently by dairy and beef producers.

Accompanying this industrialization, several worker health and social concerns have developed. In most Western countries, farms are getting fewer in number but larger in size. There are fewer family farms (combined labour and management) and more corporate structures (particularly in North America). The result is that there are more hired workers and relatively fewer family members working. Additionally, in North America, more workers are coming from minority and immigrant groups. Therefore, there is a risk of producing a new underclass of workers in some segments of the industry.

A whole new set of occupational hazardous exposures has arisen for the agricultural worker. These can be categorized under four main headings:

1.     toxic and asphyxiating gases

2.     bioactive aerosols of particulates

3.     infectious diseases

4.     noise.

Respiratory hazards are also a concern.

Toxic and Asphyxiating Gases

Several toxic and asphyxiating gases resulting from microbial degradation of animal wastes (urine and faeces) may be associated with livestock confinement. Wastes are most commonly stored in liquid form under the building, over a slatted floor or in a tank or lagoon outside the building. This manure storage system is usually anaerobic, leading to the formation of a number of toxic gases (see table 70.9) (Donham, Yeggy and Dauge 1988). See also the article “Manure and waste handling” in this chapter.

Table 70.9 Compounds identified in swine confinement building atmospheres

2-Propanol

Ethanol

Isopropyl propionate

3-Pentanone

Ethyl formate

Isovaleric acid

Acetaldehyde

Ethylamine

Methane

Acetic acid

Formaldehyde

Methyl acetate

Acetone

Heptaldehyde

Methylamine

Ammonia

Heterocylic nitrogen compound

Methylmercaptan

n-Butanol

Hexanal

Octaldehyde

n-Butyl

Hydrogen sulphide

n-Propanol

Butyric acid

Indole

Propionic acid

Carbon dioxide

Isobutanol

Proponaldehyde

Carbon monoxide

Isobutyl acetate

Propyl propionate

Decaldehyde

Isobutyraldehyde

Skatole

Diethyl sulphide

Isobutyric acid

Triethylamine

Dimethyl sulphide

Isopentanol

Trimethylamine

Disulphide

Isopropyl acetate

 

There are four common toxic or asphyxiating gases present in almost every operation where anaerobic digestion of wastes occurs: carbon dioxide (CO2), ammonia (NH3), hydrogen sulphide (H2S) and methane (CH4). A small amount of carbon monoxide (CO) may also be produced by the decomposing animal wastes, but its main source is heaters used to burn fossil fuels. Typical ambient levels of these gases (as well as particulates) in swine confinement buildings are shown in table 70.10 . Also listed are maximum recommended exposures in swine buildings based on recent research (Donham and Reynolds 1995; Reynolds et al. 1996) and threshold limit values (TLVs) set by the American Conference of Governmental Industrial Hygienists (ACGIH 1994). These TLVs have been adopted as legal limits in many countries.

Table 70.10 Ambient levels of various gases in swine confinement buildings

Gas

Range (ppm)

Typical ambient concentrations (ppm)

Recommended maximum exposure concentrations (ppm)

Threshold limit values (ppm)

CO

0 to 200

42

50

50

CO2

1,000 to 10,000

8,000

1,500

5,000

NH3

5 to 200

81

7

25

H2S

0 to 1,500

4

5

10

Total dust

2 to 15 mg/m3

4 mg/m3

2.5 mg/m3

10 mg/m3

Respirable dust

0.10 to 1.0 mg/m3

0.4 mg/m3

0.23 mg/m3

3 mg/m3

Endotoxin

50 to 500 ng/m3

200 ng/m3

100 ng/m3

(none established)

It can be seen that in many of the buildings, at least one gas, and often several, exceeds the exposure limits. It should be noted that simultaneous exposure to these toxic substances may be additive or synergistic—the TLV for the mixture may be exceeded even when individual TLVs are not exceeded. Concentrations are often higher in the winter than in the summer, because ventilation is reduced to conserve heat.

These gases have been implicated in several acute conditions in workers. H2S has been implicated in many sudden animal deaths and several human deaths (Donham and Knapp 1982). Most acute cases have occurred shortly after the manure pit has been agitated or emptied, which may result in a sudden release of a large volume of the acutely toxic H2S. In other fatal cases, manure pits had recently been emptied, and workers who entered the pit for inspection, repairs or to retrieve a dropped object collapsed without any forewarning. The available post-mortem results of these cases of acute poisoning revealed massive pulmonary oedema as the only notable finding. This lesion, combined with the history, is compatible with hydrogen sulphide intoxication. Rescue attempts by bystanders have often resulted in multiple fatalities. Confinement workers should therefore be informed of the risks involved and advised never to enter a manure storage facility without testing for the presence of toxic gases, being equipped with a respirator with its own oxygen supply, ensuring adequate ventilation and having at least two other workers stand by, attached by a rope to the worker who enters, so they can effect a rescue without endangering themselves. There should be a written confined-space programme.

CO may also be present at acute toxic levels. Abortion problems in swine at an atmospheric concentration of 200 to 400 ppm and subacute symptoms in humans, such as chronic headache and nausea, have been documented in swine confinement systems. The possible effects on the human foetus should also be of concern. The primary source of CO is from improperly functioning hydrocarbon-burning heating units. Heavy accumulation of dust in swine confinement buildings makes it difficult to keep heaters in correct working order. Propane-fuelled radiant heaters are also a common source of lower levels of CO (e.g., 100 to 300 ppm). High-pressure washers powered by an internal combustion engine that may be run inside the building are another source; CO alarms should be installed.

Another acutely dangerous situation occurs when the ventilation system fails. Gas levels may then rapidly build up to critical levels. In this case the major problem is replacement of oxygen by other gases, primarily CO2 produced from the pit as well as from the respiratory activity of the animals in the building. Lethal conditions could be reached in as few as 7 hours. Regarding the health of the pigs, ventilation failure in warm weather may allow temperature and humidity to increase to lethal levels in 3 hours. Ventilation systems should be monitored.

A fourth potentially acute hazard arises from build-up of CH4, which is lighter than air and, when emitted from the manure pit, tends to accumulate in the upper portions of the building. There have been several instances of explosions occurring when the CH4 accumulation was ignited by a pilot light or a worker’s welding torch.

Bioactive Aerosols of Particulates

The sources of dust in confinement buildings are a combination of feed, dander and hair from the swine and dried faecal material (Donham and Scallon 1985). The particulates are about 24% protein and therefore have the potential not only for initiating an inflammatory response to foreign protein but also for initiating an adverse allergic reaction. The majority of particles are smaller than 5 microns, allowing them to be respired into the deep portions of the lungs, where they may produce a greater danger to health. The particulates are laden with microbes (104 to 107/m3 air). These microbes contribute several toxic/inflammatory substances including, among others, endotoxin (the most documented hazard), glucans, histamine and proteases. The recommended maximum concentrations for dusts are listed in table 70.10 . Gases present within the building and bacteria in the atmosphere are adsorbed on the surface of the dust particles. Thus, the inhaled particles have the increased potentially hazardous effect of carrying irritating or toxic gases as well as potentially infectious bacteria into the lungs.

Infectious Diseases

Some 25 zoonotic diseases have been recognized as having occupational significance for agricultural workers. Many of these may be transmitted directly or indirectly from livestock. The crowded conditions prevailing in confinement systems offer a high potential for transmission of zoonotic diseases from livestock to humans. Swine confinement environment may offer a risk for transmission to workers of swine influenza, leptospirosis, Streptococcus suis and salmonella, for example. The poultry confinement environment may offer a risk for ornithosis, histoplasmosis, New Castle disease virus and salmonella. Bovine confinement could offer a risk for Q fever, Trichophyton verrucosum (animal ringworm) and leptospirosis.

Biologicals and antibiotics have also been recognized as potential health hazards. Injectable vaccines and various biologicals are commonly used in veterinary preventive medical programmes in animal confinement. Accidental inoculation of Brucella vaccines and Escherichia coli bacteria has been observed to cause illness in humans.

Antibiotics are commonly used both parenterally and incorporated in animal feed. Since it is recognized that feed is a common component of the dust present in animal confinement buildings, it is assumed that antibiotics are also present in the air. Thus, antibiotic hypersensitivity and antibiotic-resistant infections are potential hazards for the workers.

Noise

Noise levels of 103 dBA have been measured within animal confinement buildings; this is above the TLV, and offers a potential for noise-induced hearing loss (Donham, Yeggy and Dauge 1988).

Respiratory Symptoms of Livestock Confinement Workers

The general respiratory hazards within livestock confinement buildings are similar regardless of the species of livestock. However, swine confinements are associated with adverse health effects in a larger percentage of workers (25 to 70% of active workers), with more severe symptoms than those in poultry or cattle confinements (Rylander et al. 1989). The waste in poultry facilities is usually handled in solid form, and in this instance ammonia seems to be the primary gaseous problem; hydrogen sulphide is not present.

Subacute or chronic respiratory symptoms reported by confinement workers have been observed to be most frequently associated with swine confinement. Surveys of swine confinement workers have revealed that about 75% suffer from adverse acute upper respiratory symptoms. These symptoms can be broken down into three groups:

1.     acute or chronic inflammation of the respiratory airways (manifested as bronchitis)

2.     acquired occupational (non-allergic) constriction of the airways (asthma)

3.     delayed self-limited febrile illness with generalized symptoms (organic dust toxic syndrome (ODTS)).

Symptoms suggestive of chronic inflammation of the upper respiratory system are common; they are seen in about 70% of swine confinement workers. Most commonly, they include tightness of the chest, coughing, wheezing and excess sputum production.

In approximately 5% of workers, symptoms develop after working in the buildings for only a few weeks. The symptoms include chest tightness, wheezing and difficult breathing. Usually these workers are affected so severely that they are forced to seek employment elsewhere. Not enough is known to indicate whether this reaction is an allergic hypersensitivity or a non-allergic hypersensitivity to dust and gas. More typically, symptoms of bronchitis and asthma develop after 5 years of exposure.

Approximately 30% of workers occasionally experience episodes of delayed symptoms. Approximately 4 to 6 hours after working in the building they develop a flu-like illness manifested by fever, headache, malaise, general muscle aches and chest pain. They usually recover from these symptoms in 24 to 72 hours. This syndrome has been recognized as ODTS.

The potential for chronic lung damage certainly seems to be real for these workers. However, this has not been documented so far. It is recommended that certain procedures be followed to prevent chronic exposure as well as acute exposure to the hazardous materials in swine confinement buildings. Table 70.11  summarizes the medical conditions seen in swine confinement workers.

Table 70.11 Respiratory diseases associated with swine production

Upper airway disease

Sinusitis

Irritant rhinitis

Allergic rhinitis

Pharyngitis

Lower airway disease

Occupational asthma

Non-allergic asthma, hyperresponsive airways disease, or reactive airways disease syndrome (RADS)

Allergic asthma (IgE mediated)

Acute or subacute bronchitis

Chronic bronchitis

Chronic obstructive pulmonary disease (COPD)

Interstitial disease

Alveolitis

Chronic interstitial infiltrate

Pulmonary oedema

Generalized illness

Organic dust toxic syndrome (ODTS)

Sources: Donham, Zavala and Merchant 1984; Dosman et al. 1988; Haglind and Rylander 1987;   Harries and Cromwell 1982; Heedrick et al. 1991; Holness et al. 1987; Iverson et al. 1988;   Jones et al. 1984; Leistikow et al. 1989; Lenhart 1984; Rylander and Essle 1990;   Rylander, Peterson and Donham 1990; Turner and Nichols 1995.

Worker Protection

Acute exposure to hydrogen sulphide. Care should always be taken to avoid exposure to H2S that may be given off when agitating an anaerobic liquid manure storage tank. If the storage is under the building, it is best to stay out of the building when the emptying procedure is going on and for several hours afterwards, until air sampling indicates it is safe. Ventilation should be at the maximum level during this time. A liquid manure storage facility should never be entered without the safety measures mentioned above being followed.

Particulate exposure. Simple management procedures, such as the use of automated feeding equipment designed to eliminate as much feed dust as possible should be used to control particulate exposure. Adding extra fat to feed, frequent power-washing of the building and installing slatted flooring that cleans well are all proven control measures. An oil-misting dust-control system is presently under study and may be available in the future. In addition to good engineering control, a good-quality dust mask should be worn.

Noise. Ear protectors should be provided and worn, particularly when working in the building in order to vaccinate the animals or for other management procedures. A hearing conservation programme should be instituted.

ANIMAL HUSBANDRY

Dean T. Stueland and Paul D. Gunderson

Animal husbandry—the rearing and use of animals—involves a wide variety of activities, including breeding, feeding, moving animals from one location to another, basic care (e.g., hoof care, cleaning, vaccinations), care for injured animals (either by animal handlers or veterinarians) and activities associated with particular animals (e.g., milking of cows, shearing of sheep, working with draught animals).

Such handling of livestock is associated with a variety of injuries and illnesses among humans. These injuries and illnesses may be due to direct exposure or may be due to environmental contamination from animals. The risk of injury and illness is dependent largely on the type of livestock. The risk of injury also depends on the particulars of animal behaviour (see also the articles in this chapter on specific animals). In addition, persons associated with animal husbandry are often more likely to consume products from the animals. Finally, the specific exposures depend on methods of handling livestock, which have emerged from geographical and social factors that vary across human society.

Hazards and Precautions

Ergonomic Risks

Personnel who work with cattle often have to stand, reach, bend or exert physical effort in sustained or unusual positions. Livestock workers do have an increased risk of joint pain of the back, hips and knees. There are several activities that place the livestock worker at ergonomic risk. For example, assisting with birthing of a large animal may put the farmworker in an unusual and strained position, whereas with a small animal, the worker may be required to work or lie in an inclement environment. Further, the worker may be injured by assisting animals who are ill and whose behaviour cannot be anticipated. More commonly, joint and back pain have to do with a repetitive motion, such as milking, during which the worker may crouch or kneel repeatedly.

Other cumulative trauma diseases are recognized in farmworkers, particularly livestock workers. These may be due to repetitive motion or frequent small injuries.

Solutions to reduce ergonomic risk include intensified educational efforts focused upon appropriate handling of animals, as well as engineering efforts to redesign the work environment and its tasks to accommodate animal and human factors.

Injuries

Animals are commonly recognized as agents of injury in surveys of injuries associated with agriculture. There are several postulated explanations for these observations. Close association between the worker and the animal, which often has unpredictable behaviour, puts the livestock worker at risk. Many livestock have superior size and strength. Injuries are often due to direct trauma from kicking, biting or crushing against a structure and often involve the worker’s lower extremity. The behaviour of workers may also contribute to risk of injury. Workers who penetrate the “flight zone” of livestock or who position themselves in livestock “blind spots” are at increased risk of injury resulting from flight reaction, butting, kicking and crushing.

Figure 70.3 Panoramic vision of cattle

Women and children are over-represented among injured livestock workers. This may be due to societal factors resulting in women and children doing more of the animal-related work, or it may be due to exaggerated size differences between the animals and worker or, in the case of children, use of handling techniques to which livestock are unaccustomed.

Specific interventions to prevent animal-associated injuries include intense educational efforts, selecting animals that are more compatible with humans, selecting workers who are less likely to agitate animals and engineering approaches that decrease the risk of exposure of humans to animals.

Zoonotic Diseases

Livestock rearing requires close association of workers and animals. Humans may become infected by organisms normally present on animals, which are rarely human pathogens. In addition, the tissues and behaviour associated with infected animals may expose workers who would experience few, if any, exposures if they were working with healthy livestock.

The relevant zoonotic diseases include numerous viruses, bacteria, mycobacteria, fungi and parasites (see table 70.12). Many zoonotic diseases, such as anthrax, tinea capitis or orf, are associated with skin contamination. In addition, contamination resulting from exposure to a diseased animal is a risk factor for rabies and tularaemia. Because livestock workers often are more likely to ingest under-treated animal products, such workers are at risk of diseases such as Campylobacter, cryptosporidiosis, salmonellosis, trichinosis or tuberculosis.

Table 70.12 Zoonotic diseases of livestock handlers

Disease

Agent

Animal

Exposure

Anthrax

Bacteria

Goats, other herbivores

Handling hair, bone or other tissues

Brucellosis

Bacteria

Cattle, swine, goats, sheep

Contact with placenta and other contaminated tissues

Campylobacter

Bacteria

Poultry, cattle

Ingestion of contaminated food, water, milk

Cryptosporidiosis

Parasite

Poultry, cattle, sheep, small mammals

Ingestion of animal faeces

Leptospirosis

Bacteria

Wild animals, swine, cattle, dogs

Contaminated water on open skin

Orf

Virus

Sheep, goats

Direct contact with mucous membranes

Psittacosis

Chlamydia

Parakeets, poultry, pigeons

Inhaled desiccated droppings

Q fever

Rickettsia

Cattle, goats, sheep

Inhaled dust from contaminated tissues

Rabies

Virus

Wild carnivores, dogs, cats, livestock

Exposure of virus-laden saliva to breaks in skin

Salmonellosis

Bacteria

Poultry, swine, cattle

Ingestion of food from contaminated organisms

Tinea capitis

Fungus

Dogs, cats, cattle

Direct contact

Trichinosis

Roundworm

Swine, dogs, cats, horses

Eating poorly cooked flesh

Tuberculosis, bovine

Mycobacteria

Cattle, swine

Ingestion of unpasteurized milk; inhalation of airborne droplets

Tularaemia

Bacteria

Wild animals, swine, dogs

Inoculation from contaminated water or flesh

The control of zoonotic diseases must focus on the route and source of exposure. Elimination of the source and/or interruption of the route are essential to disease control. For example, there must be proper disposal of the carcasses of diseased animals. Often, the human disease can be prevented by eliminating the disease in animals. Additionally, there should be adequate processing of animal products or tissues before use in the human food chain.

Some zoonotic diseases are treated in the livestock worker with antibiotics. However, routine prophylactic antibiotic usage on livestock may cause emergence of resistant organisms of general public health concern.

Blacksmithing

Blacksmithing (farrier work) involves primarily musculoskeletal and environmental injury. The manipulation of metal to be used in animal care, such as for horseshoes, does demand heavy work requiring substantial muscle activity to prepare the metal and position animal legs or feet. Furthermore, applying the created product, such as a horseshoe, to the animal in farrier work is an additional source of injury (see figure 70.4).

Figure 70.4 Blacksmith shoeing a horse in Switzerland

Often, the heat required to bend metal involves exposure to noxious gases. A recognized syndrome, metal fume fever, has a clinical picture similar to pulmonary infection and results from inhalation of fumes of nickel, magnesium, copper or other metals.

Adverse health effects associated with blacksmithing can be alleviated by working with adequate respiratory protection. Such respiratory devices include respirators or powered air-purifying respirators with cartridges and pre-filters capable of filtering acid gas/organic vapours and metal fumes. If the farrier work occurs in a fixed location, local exhaust ventilation should be installed for the forge. Engineering controls, which place distance or barricades between the animal and the worker, will reduce the risk of injury.

Animal Allergies

All animals possess antigens which are non-human and could therefore serve as potential allergens. In addition, livestock are often hosts for mites. Since there are a large number of potential animal allergies, recognition of a specific allergen requires careful and thorough disease and occupational histories. Even with such data, recognition of a specific allergen may be difficult.

The clinical expression of animal allergies may include an anaphylaxis-type picture, with hives, swelling, nasal discharge and asthma. In some patients, itching and nasal discharge may be the only symptoms.

Controlling exposure to animal allergies is a formidable task. Improved practices in animal husbandry and changes in livestock facility ventilation systems may make it less likely that the livestock handler will be exposed. However, there may be little that can be done, other than desensitization, to prevent the formation of specific allergens. In general, desensitizing a worker can be performed only if the specific allergen is adequately characterized.

ANIMAL BEHAVIOUR

Understanding what influences animal behaviour can help make for a safer work environment. Genetics and learned responses (operant conditioning) influence the way an animal behaves. Certain breeds of bulls are generally more docile than others (genetic influence). An animal that has balked or refused to enter an area, and is successful at not doing so, will likely refuse to do so the next time. On repeated tries it will get more agitated and dangerous. Animals respond to the way in which they are treated, and draw upon past experiences when reacting to a situation. Animals that are chased, slapped, kicked, hit, yelled at, frightened and so on, will naturally have a sense of fear when a human is near. Thus, it is important to do everything possible to make movement of animals successful on the first attempt and as free of stress as possible for the animal.

Domesticated animals living under fairly uniform conditions develop habits which are based on doing the same thing each day at a specific time. Confining bulls in a paddock and feeding them allows them to get used to humans and can be utilized with bull-confinement mating systems. Habits are also caused by regular changes in environmental conditions, such as temperature or humidity fluctuations when daylight turns to darkness. Animals are most active at the time of greatest change, which is at dawn or dusk, and least active either in the middle of the day or the middle of the night. This factor can be used to advantage in the movement or working of animals.

Like animals in the wild, domesticated animals can protect territories. During feeding, this can appear as aggressive behaviour. Studies have shown that feed distributed in large, unpredictable patches eliminates territorial behaviour in livestock. When feed is distributed uniformly or in predictable patterns, it may result in fighting by animals to secure the feed and exclude others. Territorial protection may also occur when a bull is permitted to remain with the herd. The bull may view the herd and the range they cover as his territory, which means he will defend it against perceived and real threats, such as humans, dogs and other animals. Introducing a new or strange bull of breeding age into the herd almost always results in fighting to establish the dominant male.

Bulls, due to having their eyes on the side of their head, have panoramic vision and very little depth perception. This means they can see about 270° around them, leaving a blind spot directly behind them and right in front of their noses (see figure 70.3). Sudden or unexpected movements from behind can “spook” the animal because it cannot determine the proximity or seriousness of the perceived threat. This can cause a “flight or fight” response in the animal. Because cattle have poor depth perception, they can also be easily frightened by shadows and movements outside of working or holding areas. Shadows falling within the working area may appear as a hole to the animal, which can cause it to balk. Cattle are colour blind, but do perceive colours as different shades of black and white.

Many animals are sensitive to noise (compared with humans), especially at high frequencies. Loud, abrupt noises, such as metal gates clanging shut, head chutes latching and/or humans yelling can cause stress in the animals.

David L. Hard

MANURE AND WASTE HANDLING

William Popendorf

The importance of the management of waste has increased as the intensity of agricultural production on farms has increased. Waste from livestock production is dominated by manure, but also includes bedding and litter, wasted feed and water and soil. Table 70.13  lists some relevant characteristics of manure; human waste is included both for comparison and because it too must be treated on a farm. The high organic content of manure provides an excellent growth medium for bacteria. The metabolic activity of bacteria will consume oxygen and maintain bulk-stored manure in an anaerobic state. Anaerobic metabolic activity can produce a number of well-known toxic gaseous by-products, including carbon dioxide, methane, hydrogen sulphide and ammonia.

Table 70.13 Physical properties of manure as excreted per day per 1,000 lb of animal weight,  excluding moisture.

 

Weight (lb)

Volume (ft3)

Volatiles (lb)

Moisture (%)

+

    

As excreted

As stored

Dairy cow

80–85

1.3

1.4–1.5

85–90

>98

Beef cow

51–63

0.8–1.0

5.4–6.4

87–89

45–55

Pig (grower)

63

1.0

5.4

90

91

Sow (gestation)

27

0.44

2.1

91

97

Sow and piglets

68

1.1

6.0

90

96

Laying hens

60

0.93

10.8

75

50

Broilers

80

1.3

15.

75

24

Turkeys

44

0.69

9.7

75

34

Lamb (sheep)

40

0.63

8.3

75

Human

30

0.55

1.9

89

99.5

Source: USDA 1992.

Management Processes

The management of manure involves its collection, one or more transfer operations, storage or/and optional treatment and eventually utilization. The moisture content of manure as listed in table 70.13  determines its consistency. Wastes of different consistencies require different management techniques and therefore can present different health and safety hazards (USDA 1992). The reduced volume of solid or low-moisture manure generally permits lower equipment costs and energy requirements, but handling systems are not easily automated. The collection, transfer and any optional treatments of liquid waste are more easily automated and require less daily attention. Storage of manure becomes increasingly mandatory as the seasonal variability of the local crops increases; the storage method must be sized to meet the production rate and utilization schedule while preventing environmental damage, especially from water runoff. Options for utilization include use as plant nutrients, mulch, animal feed, bedding or a source to produce energy.

Manure Production

Dairy cows are typically raised on pastures, except when in holding areas for pre- and post-milking and during seasonal extremes. Water use for cleaning in milking operations can vary from 5 to 10 gallons per day per cow, where flushing of wastes is not practised, to 150 gallons per day per cow where it is. Therefore, the method used for cleaning has a strong influence on the method chosen for manure transport, storage and utilization. Because the management of beef cattle requires less water, beef manure is more often handled as a solid or semi-solid. Composting is a common storage and treatment method for such dry wastes. The local precipitation pattern also strongly influences the preferred waste management scheme. Excessively dry feedlots are apt to produce a downwind dust and odour problem.

The major problems for swine raised on traditional pastures are the control of runoff and soil erosion due to the gregarious nature of pigs. One alternative is the construction of semi-enclosed pig buildings with paved lots, which also facilitates the separation of solid and liquid wastes; solids require some manual transfer operations but liquids can be handled by gravity flow. Waste-handling systems for fully enclosed production buildings are designed to collect and store waste automatically in a largely liquid form. Livestock playing with their watering facilities can increase the volumes of swine waste. Manure storage is generally in anaerobic pits or lagoons.

Poultry facilities are generally divided into those for meat (turkeys and broilers) and egg (layers) production. The former are raised directly on prepared litter, which maintains the manure in a relatively dry state (25 to 35% moisture); the only transfer operation is mechanical removal, generally only once per year, and transport directly to the field. Layers are housed in stacked cages without litter; their manure can either be allowed to collect in deep stacks for infrequent mechanical removal or be automatically flushed or scraped in a liquid form much like swine manure.

The consistency of waste from most other animals, like sheep, goats and horses, is largely solid; the major exception is veal calves, because of their liquid diet. Waste from horses contains a high fraction of bedding and may contain internal parasites, which limits its utilization on pasture land. Waste from small animals, rodents and birds may contain disease organisms that can be transmitted to humans. However, studies have shown that faecal bacteria do not survive on forage (Bell, Wilson and Dew 1976).

Storage Hazards

Storage facilities for solid wastes must still control water runoff and leaching into surface and ground water. Thus, they should be paved pads or pits (that may be seasonal ponds) or covered enclosures.

Liquid and slurry storage is basically limited to ponds, lagoons, pits or tanks either below or above ground. Long-term storage is coincident with onsite treatment, usually by anaerobic digestion. Anaerobic digestion will reduce the volatile solids indicated in table 70.13 , which also reduces odours emanating from eventual utilization. Unguarded below-surface holding facilities can lead to injuries or fatalities from accidental entry and falls (Knoblauch et al. 1996).

The transfer of liquid manure presents a highly variable hazard from mercaptans produced by anaerobic digestion. Mercaptans (sulphur-containing gases) have been shown to be major contributors to the odour of manure and are all quite toxic (Banwart and Brenner 1975). Perhaps the most dangerous of the effects from H2S shown in table 70.14  is its insidious capacity to paralyze the sense of smell in the 50- to 100-ppm range, removing the sensory capacity to detect higher, rapidly toxic levels. Liquid storage for as short as 1 week is enough to initiate the anaerobic production of toxic mercaptans. Major differences in long-term manure gas generation rates are thought to be due to uncontrolled variations in the chemical and physical differences within the stored manure, such as temperature, pH, ammonia and organic loading (Donham, Yeggy and Dauge 1985).

Table 70.14 Some important toxicologic benchmarks for hydrogen sulphide (H2S)

Physiological or regulatory benchmark

Parts per million (ppm)

Odour detection threshold (rotten-egg smell)

.01–.1

Offensive odour

3–5

TLV-TWA = recommended exposure limit

10

TLV-STEL = recommended 15-minute exposure limit

15

Olfactory paralysis (cannot be smelled)

50–100

Bronchitis (dry cough)

100–150

IDLH (pneumonitis and pulmonary oedema)

100

Rapid respiratory arrest (death in 1–3 breaths)

1,000–2,000

TLV-TWA = Threshold limit values–Time weighted average; STEL = Short-term exposure level;  IDLH = Immediately dangerous to life and health.

The normally slow release of these gases during storage is greatly increased if the slurry is agitated to resuspend the sludge that accumulates at the bottom. H2S concentrations of 300 ppm have been reported (Panti and Clark 1991), and 1,500 ppm has been measured during the agitation of liquid manure. The rates of gas release during agitation are much too large to be controlled by ventilation. It is most important to realize that natural anaerobic digestion is uncontrolled and therefore highly variable. The frequency of serious and fatal over-exposures can be predicted statistically but not at any individual site or time. A survey of dairy farmers in Switzerland reported a frequency of about one manure gas accident per 1,000 person-years (Knoblauch et al. 1996). Safety precautions are necessary each time agitation is planned to avoid the unusually hazardous event. If the operator does not agitate, sludge will build up until it may have to be removed mechanically. Such sludge should be left to dry before someone physically enters an enclosed pit. There should be a written confined-space programme.

Rarely used alternatives to anaerobic ponds include an aerobic pond, a facultative pond (one using bacteria that can grow under both aerobic and anaerobic conditions), drying (dewatering), composting or an anaerobic digester for biogas (USDA 1992). Aerobic conditions can be created either by keeping the liquid depth no more than 60 to 150 cm or by mechanical aeration. Natural aeration takes more space; mechanical aeration is more costly, as are the circulating pumps of a facultative pond. Composting may be conducted in windrows (rows of manure which must be turned every 2 to 10 days), a static but aerated pile or a specially constructed vessel. The high nitrogen content of manure must be reduced by mixing a high carbon amendment that will support the thermophilic microbial growth necessary for composting to control odours and remove pathogens. Composting is an economical method of treating small carcasses, if local ordinances permit. See also the article “Waste disposal operations” elsewhere in this Encyclopaedia. If a rendering or disposal plant is not available, other options include incineration or burial. Their prompt treatment is important to control herd or flock disease. Swine and poultry wastes are particularly amenable to methane production, but this utilization technique is not widely adopted.

Thick crusts can form on top of liquid manure and appear solid. A worker may walk on this crust and break through and drown. Workers can also slip and fall into liquid manure and drown. It is important to keep rescue equipment near the liquid manure storage site and avoid working alone. Some manure gases, such as methane, are explosive, and “no smoking” signs should be posted in or around the manure storage building (Deere & Co. 1994).

Application Hazards

Transfer and utilization of dry manure can be by hand or with mechanical aids like a front-end loader, skid-steer loader and manure spreader, each of which presents a safety hazard. Manure is spread onto land as fertilizer. Manure spreaders are generally pulled behind a tractor and powered by a power-take-off (PTO) from the tractor. They are classified into one of four types: box-type with rear beaters, flail, V-tank with side discharge and closed tank. The first two are used to apply solid manure; the V-tank spreader is used to apply liquid, slurry or solid manure; and the closed tank spreader is used to apply liquid manure. The spreaders throw the manure over large areas either to the rear or sides. Hazards include the machinery, falling objects, dust and aerosols. Several safety procedures are listed in table 70.15 .

Table 70.15 Some safety procedures related to manure spreaders

1. Only one person should operate the machine to avoid inadvertent activation by another person.

2. Keep workers clear of active power-take offs (PTOs), beaters, augers and expellers.

3. Maintain all guards and shields.

4. Keep persons clear of rear and sides of the spreader, which can project heavy objects mixed into the manure as far as 30 m.

5. Avoid dangerous unplugging operations by preventing spreader plugging:

  • Keep stones, boards and other objects out of the spreader.
  • In freezing weather, make sure flails and chains on flail-type spreaders are loose and unfrozen before operation.
  • Keep chains and beaters on beater-type spreaders in good operating order by replacing stretched chains and avoiding dropping loads of frozen manure onto the spreader chains.
  • Never get into an operating spreader to clean it.
  • Maintain the unloading auger and discharge expeller on V-tank spreaders so they operate freely.
  • In cold weather, clean the spreader insides so wet manure will not freeze the moving parts.

6. Use good tractor and PTO safety practices.

7. Make sure the relief valve on closed-tank spreaders is operative to avoid excessive pressures.

8. When unhooking the spreader from the tractor, make sure the jack that holds the weight of the spreader tongue is secure and locked to prevent the spreader from falling.

9. When the spreader is creating airborne dust or aerosols, use respiratory protection.

Source: Deere & Co. 1994.

A CHECKLIST FOR LIVESTOCK REARING SAFETY PRACTICES

Feeding

1.     Use proper ventilation in buildings and silos.

2.     Keep entrances to grain, feed and silage storage areas closed and locked.

3.     Post warning signs in feed and silage storage areas about the hazard of entrapment in flowing grain or feed.

4.     Maintain silo and bin ladders in good condition.

5.     Shield auger inlets to prevent contact with augers.

6.     Cover loading troughs on augers, elevators and conveyors with grating.

7.     Use caution when moving augers and elevators; check for overhead power lines.

8.     Assure that shields are in place for all feeding, grinding and other equipment.

9.     Be aware of health effects of breathing organic dust, and inform your doctor about recent dust exposure when seeking treatment for respiratory illness.

10.     Use automated or mechanized equipment to move decayed materials.

11.     Use source containment, local exhaust ventilation and wet methods to control organic dust.

12.     Use appropriate respiratory protection when dust exposure is unavoidable.

Handling

1.     Establish good sanitation, vaccination and inoculation programmes.

2.     When working with animals, plan an escape exit; have at least two ways out.

3.     Livestock handlers should have enough strength and experience for the job.

4.     Avoid working with animals when you are tired.

5.     Use caution when approaching animals so as not to startle them.

6.     Know the animals and be patient with them.

7.     Dehorn dangerous animals.

8.     Post warning signs where chemicals are stored; lock them in a room or cabinet.

9.     Mix all chemicals outside or in a well-ventilated area.

10.     Be careful when leading animals.

11.     Wear rubber gloves when treating sick animals.

12.     Vaccinate animals, and quarantine sick animals.

13.     Wash hands after contact with calves with diarrhoea (scours).

Containment and housing

1.     Make sure all pens, gates, loading chutes and fences are in good repair and strong enough to contain the animal.

2.     Do not allow tobacco smoking around farm buildings and fuel storage and refueling areas; post “no smoking” signs in these areas.

3.     Maintain fully charged ABC-type fire extinguishers in major farm buildings.

4.     Remove trash and debris around buildings to prevent fires and falls.

5.     Keep all buildings in good repair.

6.     Keep electrical wiring in good condition.

7.     Use adequate lighting in all buildings.

8.     Keep floors clean and free of broken concrete and slippery areas.

Waste disposal

1.     Correctly dispose of all chemical containers following directions on the label.

2.     Install vent pipes and exhaust fans in manure pits.

Melvin L. Myers

DAIRY

John May

The dairy farmer is a livestock specialist whose aim is optimizing the health, nutrition and reproductive cycling of a herd of cows with the ultimate goal of maximal milk production. Major determinants of the farmer’s exposure to hazards are farm and herd size, labour pool, geography and degree of mechanization. A dairy farm may be a small family business milking 20 or fewer cows per day, or it may be a corporate operation using three shifts of workers to feed and milk thousands of cows around the clock. In regions of the world where the climate is quite mild, the cattle may be housed in open sheds with roofs and minimal walls. Alternatively, in some regions barns must be tightly closed to preserve sufficient heat to protect the animals and the watering and milking systems. All of these factors contribute variability to the risk profile of the dairy farmer. Nevertheless, there are a series of hazards which most people working in dairy farming around the world will encounter to at least some degree.

Hazards and Precautions

Noise

One potential hazard which clearly relates to the degree of mechanization is noise. In dairy farming, harmful noise levels are common and always related to some type of mechanical device. Leading offenders outside of the barn are tractors and chain-saws. Noise levels from these sources are often at or above the 90-100 dBA range. Within the barn, other noise sources include bedding choppers, small skid-steer loaders and milking pipeline vacuum pumps. Here again, sound pressures may exceed those levels generally considered to be damaging to the ear. Although the studies of noise-induced hearing loss in dairy farmers are limited in number, they combine to show a convincing pattern of hearing deficits affecting predominantly the higher frequencies. These losses can be quite substantial and occur considerably more frequently in farmers of all ages than in non-farm controls. In several of the studies, the losses were more notable in the left than the right ear—possibly because farmers spend much of their time with the left ear turned toward the engine and muffler when driving with an implement. Prevention of these losses may be accomplished by efforts directed at noise abatement and muffling, and institution of a hearing-conservation programme. Certainly, the habit of wearing hearing protective devices, either muffs or earplugs, may help substantially to reduce the next generation’s risk of noise-induced hearing loss.

Chemicals

The dairy farmer has contact with some chemicals which are commonly found in other types of agriculture, as well as some which are specific to the dairy industry, such as those used for cleaning the automated vacuum-powered milking pipeline system. This pipeline must be effectively cleaned before and after each use. Commonly this is done by first flushing the system with a very strong alkaline soap solution (typically 35% sodium hydroxide), followed by an acidic solution such as 22.5% phosphoric acid. A number of injuries have been observed in association with these chemicals. Spills have resulted in significant skin burns. Splatters may injure the cornea or conjunctivae of unprotected eyes. Tragic accidental ingestion—often by young children—which may occur when these materials are pumped into a cup and then briefly left unattended. These situations can be best prevented by the use of an automated, closed flush system. In the absence of an automated system, precautions must be taken to restrict access to these solutions. Measuring cups should be clearly labelled, reserved for only this purpose, never left unattended and rinsed thoroughly after each use.

Like others working with livestock, dairy farmers may have exposure to a variety of pharmaceutical agents ranging from antibiotics and progestational agents to prostaglandin inhibitors and hormones. Depending upon the country, dairy farmers also may use fertilizers, herbicides and insecticides with varying degrees of intensity. In general, the dairy farmer uses these agrochemicals less intensively than persons working in some other types of farming. However, the same care in mixing, applying and storing these materials is necessary. Appropriate application techniques and protective garb are as important for the dairy farmer as anyone else working with these compounds.

Ergonomic Risks

Although data on the prevalence of all musculoskeletal problems are currently incomplete, it is clear that dairy farmers have increased risk of arthritis of the hip and knee compared to nonfarmers. Similarly, their risk of back problems may also be elevated. Although not well studied, there is little question that ergonomics is a major problem. The farmer may routinely carry weights in excess of 40 kg—often in addition to considerable personal body weight. Tractor driving produces abundant vibration exposure. However, it is the portion of the job devoted to milking that seems most ergonomically significant. A farmer may bend or stoop 4 to 6 times in the milking of a single cow. These motions are repeated with each of a number of cows twice daily for decades. Carrying the milking equipment from stall to stall imposes an additional ergonomic load on the upper extremities. In countries where milking is less mechanized, the ergonomic load on the dairy farmer might be different, but still it is likely to reflect considerable repetitive strain. A potential solution in some countries is the shift to milking parlours. In this setting the farmer can milk a number of cows simultaneously while standing several feet below them in the central pit of the parlour. This eliminates the stooping and bending as well as the upper-extremity load of carrying equipment from stall to stall. The latter problem is also addressed by the overhead track systems being introduced in some Scandinavian countries. These support the weight of the milking equipment when moving between stalls, and can even provide a convenient seat for the milker. Even with these potential solutions, much remains to be learned about ergonomic problems and their resolution in dairy farming.

Dust

A closely linked problem is organic dust. This is a complex, often allergenic and generally ubiquitous material on dairy farms. The dust frequently has high concentrations of endotoxin and may contain beta-glucans, histamine and other biologically active materials (Olenchock et al. 1990). Levels of total and respirable dust may exceed 50 mg/m3 and 5 mg/m3, respectively, with certain operations. These most commonly involve work with microbially contaminated feed or bedding within a closed space such as a barn, hay loft, silo or grain bin. Exposure to these dust levels may result in acute problems such as ODTS or hypersensitivity pneumonitis (“farmer’s lung disease”). Chronic exposure may also play a role in asthma, farmer’s lung disease and chronic bronchitis, which seems to occur at twice the rate of a non-farm population (Rylander and Jacobs 1994). The prevalence rates of some of these problems are higher in settings where moisture levels in the feed are likely to be elevated and in areas where barns are more tightly closed because of climatic requirements. Various farming practices such as drying of the hay and shaking out of feed for the animals by hand, and the choice of bedding material, can be major determinants of the levels of both the dust and its associated illnesses. Farmers can often devise a number of techniques to minimize either the amount of microbial overgrowth or its subsequent aerosolization. Examples include the use of sawdust, newspapers and other alternative materials for bedding instead of moulded hay. If hay is used, the addition of a quart of water to the cut surface of the bale minimizes the dust generated by a mechanical bedding chopper. Capping vertical silos with plastic sheets or tarpaulins without additional feed on top of this layer minimizes the dust of subsequent uncapping. The use of small amounts of moisture and/or ventilation in situations where dust is likely to be generated is often possible. Finally, farmers must anticipate potential dust exposures and use appropriate respiratory protection in these situations.

Allergens

Allergens may represent a troublesome health challenge for some dairy farmers. Major allergens appear to be those encountered in the barns, typically animal danders and “storage mites” living in feed stored within the barns. One study has extended the storage mite problem beyond the barn, finding sizeable populations of these species living within farmhouses as well (van Hage-Hamsten, Johansson and Hogland 1985). Mite allergy has been confirmed as a problem in a number of parts of the world, often with differing species of mites. Reactivity to these mites, to cow dander and to multiple other less significant allergens, results in several allergic manifestations (Marx et al. 1993). These include immediate onset of nasal and eye irritation, allergic dermatitis and, of greatest concern, allergy-mediated occupational asthma. This can occur as either an immediate or delayed (up to 12 hours) reaction and may occur in individuals not previously known to be asthmatic. It is of concern because the dairy farmer’s involvement in barn activities is daily, intensive and lifelong. With this nearly continual allergic re-challenge, progressively more severe asthma is likely to be seen in some farmers. Prevention includes avoidance of dust, which is the most effective and, unfortunately, the most difficult intervention for most dairy farmers. The results of medical therapies, including allergy shots, topical steroids or other anti-inflammatory agents, and symptomatic relief with bronchodilators, have been mixed.

CATTLE, SHEEP AND GOATS

Melvin L. Myers*

*Material on hair-cutting and shearing was written with the assistance of J.F. Copplestone’s article on the subject in the 3rd edition of this Encyclopaedia.

Several animals convert high-fibre feeds, called roughage (over 18% fibre), into edible food that is consumed by humans. This ability comes from their four-stomach digestion system, which includes their largest stomach, the rumen (for which they gain the designation ruminants) (Gillespie 1997). Table 70.16  shows the various types of ruminant livestock that have been domesticated and their uses.

Table 70.16 Types of ruminants domesticated as livestock

Ruminant type

Uses

Cattle

Meat, milk, draught

Sheep

Meat, wool

Goats

Meat, milk, mohair

Camelids (llama, alpaca, dromedary and bactrian camels)

Meat, milk, hair, draught

Buffalo (water buffalo)

Meat, draught

Bison

Meat

Yaks

Meat, milk, wool

Reindeer

Meat, milk, draught

Production Processes

Processes for rearing ruminants vary from intensive, high-production operations such as raising beef cattle on large, 2,000-km2 ranches in Texas to communal grazing such as the nomadic herders of Kenya and the United Republic of Tanzania. Some farmers use their cattle as oxen for traction power in farm tasks such as ploughing. In humid areas, water buffalo serve the same purpose (Ker 1995). The trend is toward high-production, intensive systems (Gillespie 1997).

High-volume, intensive beef production depends on various interdependent operations. One is the cow-calf system, which involves keeping a herd of cows. The cows are bred by bulls or artificial insemination annually to produce calves, and, after weaning, the calves are sold to cattle feeders to raise for slaughter. Male calves are castrated for the slaughter market; a castrated calf is called a steer. Pure-bred breeders maintain the herds of breeding stock, including bulls, which are very dangerous animals.

Sheep are produced in either range or farm flocks. In range production, flocks of 1,000 to 1,500 ewes are common. In farm flocks, production is usually small and typically a secondary enterprise. Sheep are raised for their wool or as feeder lambs for the slaughter market. Lambs are docked, and most male lambs are castrated. Some enterprises specialize in raising rams for pure-bred breeding.

Goats are raised through either range or small-farm production for their mohair, milk and meat. Pure-bred breeders are small operations that raise rams for breeding does. Specific breeds exist for each of these products. The goats are dehorned, and most males are castrated. Goats browse on shoots, twigs and leaves of brush plants, and thus they may also be used to control brush on a ranch or farm.

Other major processes involved in rearing cattle, sheep and goats include feeding, disease and parasite control, hair clipping and fleece shearing. The milking process and livestock waste disposal are addressed in other articles in this chapter.

Cattle, sheep and goats are fed in several ways, including grazing or feeding hay and silage. Grazing is the least expensive way to deliver forage to animals. Animals typically graze on pastures, wild lands or crop residues, such as corn stalks, which remain in the field after crop harvests. Hay is harvested from the field and typically stored loose or in stacked bales. The feeding operation includes moving the hay from the stack to the open field or into mangers to feed the animals. Some crops such as corn are harvested and converted into silage. Silage is typically moved mechanically into mangers for feeding.

The control of diseases and parasites in cattle, sheep and goats is an integral part of the livestock-rearing process and requires animal contact. Routine visits to the herd by a veterinarian are an important part of this process, as is observing vital signs. Timely vaccination against diseases and quarantining diseased animals are also important.

External parasites include flies, lice, mange, mites and ticks. Chemicals are one control against these parasites. Pesticides are applied by spraying or through insecticide-impregnated ear tags. The heel fly lays eggs on the hair of cattle, and its larva, the cattle grub, burrows into the skin. A control for this grub is systemic pesticides (spread throughout the body through spray, dips or as a feed additive). Internal parasites, including roundworms or flatworms, are controlled with drugs, antibiotics or drenches (oral administration of a liquid medication). Sanitation is also a strategy for the control of infectious diseases and parasite infestations (Gillespie 1997).

The removal of hair from live animals helps to maintain their cleanliness or comfort and to prepare them for exhibitions. Hair may be sheared from live animals as a product, such as the fleece from sheep or mohair from goats. The sheep shearer catches the animal in a pen and drags it to a stand where it is laid on its back for the shearing operation. It is pinned by the shearer’s legs. Hair cutters and sheep shearers use a hand-operated scissors or motorized shears to clip the hair. The motorized shears are typically powered by electricity. Prior to shearing and also as part of gestation management, sheep are tagged and crutched (i.e., hair encrusted with faeces is removed). The cut fleece is manually trimmed according to the quality and staple of the hair. It is then compressed into packs for transportation using a hand-operated screw or hydraulic ram.

Facilities used for raising cattle, sheep and goats are generally considered to be either confined or unconfined. Confined facilities include confinement houses, feedlots, barns, corrals (holding, sorting and crowding pens), fences and working and loading chutes. Unconfined facilities refer to pasture or range operations. Feeding facilities include storage facilities (vertical and horizontal silos), feed grinding and mixing equipment, haystacks, conveying equipment (including augers and elevators), feed bunks, water fountains and mineral and salt feeders. In addition, sun protection may be provided by sheds, trees or overhead lattice work. Other facilities include back rubbers for parasite control, creep-feeders (allows feeder calves or lambs to feed without adults feeding), self-feeders, calf shelters, cattle-guard gates and cattle treatment stalls. Fencing may be used around pastures, and these include barbed wire and electric fences. Woven wire may be required to contain goats. Free-ranging animals would require herding to control their movement; goats may be tethered, but require shade. Dipping tanks are used for parasite control in large sheep flocks (Gillespie 1997).

Hazards

Table 70.17 shows several other processes of cattle, sheep and goat handling, with associated hazardous exposures. In a survey of farm workers in the United States (Meyers 1997), handling livestock represented 26% of lost-time injuries. This percentage was higher than any other farm activity, as shown in figure 70.5 . These figures would be expected to be representative of the injury rate in other industrialized countries. In countries where draught animals are common, injury rates would be expected to be higher. Injuries from cattle usually occur in farm buildings or in the vicinity of buildings. Cattle inflict injuries when they kick or step on people or crush them against a hard surface such as the side of a pen. People may also be injured by falling when working with cattle, sheep and goats. Bulls inflict the most serious injuries. Most of the people injured are family members rather than hired workers. Fatigue can reduce judgement, and thus increase the chance of injury (Fretz 1989).

Table 70.17 Livestock rearing processes and potential hazards

Process

Potential hazardous exposures

Breeding, artificial inseminating

Violent acts by bulls, rams or bucks; slips and falls;   zoonoses; organic dust and dander

Feeding

Organic dust; silo gas; machines; lifting; electricity

Calving, lambing, kidding

Lifting and pulling; animal behaviour

Castrating, docking

Animal behaviour; lifting; cuts from knives

Dehorning

Animal behaviour; cuts from trimmers; caustic   salves; burns from electric irons

Branding and marking

Burns; animal behaviour

Vaccinating

Animal behaviour; needle sticks

Spraying and dusting/drenching, worming

Organophosphates

Foot/hoof trimming

Animal behaviour; awkward postures; tool-related   cuts and pinches

Shearing, tagging and crutching, washing and clipping

Awkward postures and lifting; animal behaviour;   hand-shearer cuts; electricity

Loading and unloading

Animal behaviour

Manure handling

Manure gases; slips and falls; lifting; machines

Sources: Deere & Co. 1994; Fretz 1989; Gillespie 1997; NIOSH 1994.

Figure 70.5 Estimates of lost-time injury frequency by farm activity in the United States, 1993

Source: Meyers 1997.

Livestock exhibit behaviours that can lead to injuries of workers. The herding instinct is strong among animals such as cattle or sheep, and imposed limits such as isolation or overcrowding can lead to unusual behavioural patterns. Reflexive response is a common defensive behaviour among animals, and it can be predicted. Territorialism is another behaviour that is predictable. A reflexive escape struggle is apparent when an animal is removed from its normal quarters and placed in a confined environment. Animals that are restrained by chutes for loading for transportation will exhibit agitated reflex response behaviour.

Dangerous environments are numerous in cattle, sheep and goat production facilities. These include slippery floors, manure pits, corrals, dusty feed areas, silos, mechanized feeding equipment and animal confinement buildings. Confinement buildings may have manure storage pits, which can emit lethal gases (Gillespie 1997).

Heat exhaustion and stroke are potential hazards. Heavy physical labour, stress and strain, heat, high humidity and dehydration from lack of drinking water all contribute to these hazards.

Livestock handlers are at risk for developing respiratory illness from exposure to inhaled dusts. A common illness is organic dust toxic syndrome. This syndrome may follow exposures to heavy concentrations of organic dusts contaminated with micro-organisms. About 30 to 40% of workers who are exposed to organic dusts will develop this syndrome, which includes the conditions shown in table 70.18 ; this table also shows other respiratory conditions (NIOSH 1994).

Table 70.18 Respiratory illnesses from exposures on livestock farms

Organic dust toxic syndrome conditions

  • Precipitin-negative farmer’s lung disease
  • Pulmonary mycotoxicosis
  • Silo unloader’s syndrome
  • Grain fever in grain elevator workers

Other important respiratory illnesses

  • "Silo fillers’ disease" (acute toxic inflammation of the lung)
  • "Farmer’s lung disease" (hypersensitivity pneumonitis)
  • Bronchitis
  • Asphyxiation (suffocation)
  • Toxic gas inhalation (for example, manure pits)

Hair cutters and sheep shearers face several hazards. Cuts and abrasions may result during the shearing operation. Animal hoofs and horns also present potential hazards. Slips and falls are an ever-present hazard while handling the animals. Power for the shears is sometimes transferred by belts, and guards must be maintained. Electrical hazards are also present. Shearers also face postural hazards, particularly to the back, as a result of catching and tipping the sheep. Constraining the animal between the shearer’s legs tends to strain the back, and torsional movements are common while shearing. Manual shearing usually results in tenosynovitis.

The control of insects on cattle, sheep and goats with pesticide spray or powder can expose workers to the pesticide. Sheep dips submerge the animal in a pesticide bath, and handling the animal or contact with the bath solution or contaminated wool can also expose workers to the pesticide (Gillespie 1997).

Common zoonoses include rabies, brucellosis, bovine tuberculosis, trichinosis, salmonella, leptospirosis, ringworm, tapeworm, orf virus disease, Q fever and spotted fever. Diseases that may be contracted while working with hair and fleece include tetanus, salmonellosis from tagging and crutching, leptospirosis, anthrax and parasitic diseases.

Animal faeces and urine also provide a mechanism for infection of workers. Cattle are a reservoir for cryptosporidosis, a disease that can be transmitted from cattle to humans through the faecal-oral route. Calves with diarrhoea (scours) may harbour this disease. Schistosomiasis, an infection by blood flukes, is found in cattle, water buffalo and other animals in several parts of the world; its life cycle goes from eggs excreted in urine and faeces, developing into larvae, which enter snails, then to free-swimming cercariae that attach to and penetrate human skin. Penetration can occur while workers are wading in water.

Some zoonoses are arthropod-borne viral diseases. The primary vectors for these diseases are mosquitoes, ticks and sandflies. These diseases include arboviral encephalitides transmitted by ticks and milk from sheep, babesiosis transmitted by ticks from cattle and Crimean-Congo haemorrhagic fever (Central Asian haemorrhagic fever) transmitted by mosquitoes and ticks from cattle, sheep and goats (as amplifying hosts) during epizootics (Benenson 1990; Mullan and Murthy 1991).

Preventive Action

The principal occupational hazards that occur in rearing ruminants include injuries, respiratory problems and zoonotic diseases. (See “A checklist for livestock rearing safety practices”.)

Stair steps should be maintained in good condition, and floors must be even to reduce fall hazards. Guards on belts, mechanical screws, compression rams and shear sharpening equipment should be maintained. Wiring should be maintained in good condition to prevent electrical shock. Ventilation should be assured wherever internal combustion engines are used in barns.

Training and experience in properly handling animals helps to prevent injuries related to the animals’ behaviour. Safe livestock handling requires understanding of both innate and acquired components of animal behaviour. Facilities should be designed so workers do not have to enter small or enclosed areas with animals. Lighting should be diffuse, since animals may become confused and balk around bright lights. Sudden noises or movements may startle cattle, causing them to crowd a person against hard surfaces. Even clothing hanging on fences flapping in the wind can startle cattle. They should be approached from the front so as not to surprise them. Avoid use of contrasting patterns in cattle facilities, because cattle will slow or stop when they see these patterns. Shadows across the floor should be avoided because cattle may refuse to cross over them (Gillespie 1997).

Risks of organic dust exposure can be minimized in several ways. Workers should be aware of the health effects of breathing organic dust and inform their physician about recent dust exposures when seeking help for respiratory illness. Minimizing spoilage of feed can minimize potential fungal spore exposures. To avoid such hazards, workers should use mechanized equipment to move decaying materials. Farm operators should use local exhaust ventilation and wet methods of dust suppression to minimize exposure. Appropriate respirators should be worn when organic dust exposure cannot be avoided (NIOSH 1994).

Preventing zoonoses depends upon maintaining clean livestock facilities, vaccinating the animals, quarantine of sick animals and avoiding exposure to sick animals. Rubber gloves should be worn when treating sick animals to avoid exposures through any cuts in the hands. Workers who become sick after contact with a sick animal should seek medical help (Gillespie 1997).

PIGS

Melvin L. Myers

Pigs were primarily domesticated from two wild stocks—the European wild boar and the East Indian pig. The Chinese domesticated the pig as early as 4900 BC, and today more than 400 million pigs are reared in China out of 840 million worldwide (Caras 1996).

Pigs are reared primarily for food and have many distinguishing attributes. They grow fast and large, and the sows have large litters and short gestation periods of about 100 to 110 days. Pigs are omnivores and eat berries, carrion, insects and garbage, as well as the corn, silage and pasture of high-production enterprises. They convert 35% of their feed into meat and lard, which is more efficient than ruminant species such as cattle (Gillespie 1997).

Production Processes

Some pig holdings are small—for example, one or two animals, which can represent much of a family’s wealth (Scherf 1995). Large pig operations include two major processes (Gillespie 1997).

One process is pure-bred production, in which pig breeding stock are improved. Within the pure-bred operation, artificial insemination is prevalent. Pure-bred boars are typically used to breed sows in the other major process, commercial production. The commercial production process rears pigs for the slaughter market and typically follows one of two different types of operations. One operation is a two-stage system. The first stage is feeder pig production, which uses a herd of sows to farrow litters of 14 to 16 piglets per sow. The pigs are weaned, then sold to the next stage of the system, the buying and finishing enterprise, which feeds them for the slaughter market. The most common feeds are corn and soybean oil meal. The feed grains are typically ground.

The other and most common operation is the complete sow and litter system. This production operation rears a herd of breeding sows and farrowing pigs, caring for and feeding the farrowed pigs for the slaughter market.

Some sows give birth to a litter that may outnumber her teats. To feed the excess piglets, a practice is to spread piglets from large litters into other sows’ smaller litters. Pigs are born with needle teeth, which are typically clipped at the gum-line before the pig is two days old. Ears are notched for identification. Tail docking occurs when the pig is about 3 days old. Male pigs raised for the slaughter market are castrated before they are 3 weeks old.

Maintaining a healthy herd is the single most important management practice in pig production. Sanitation and the selection of healthy breeding stock are important. Vaccination, sulpha drugs and antibiotics are used to prevent many infectious diseases. Insecticides are used to control lice and mites. The large roundworm and other parasites of pigs are controlled through sanitation and drugs.

Facilities used for pig production include pasture systems, a combination of pasture and low-investment housing and high-investment total-confinement systems. The trend is toward more confinement housing because it produces faster growth than does pasture rearing. However, pasture is valuable in feeding the pig-breeding herd to prevent fattening the breeding herd; it may be used for all or part of the production operation with the use of portable housing and equipment.

Confinement buildings require ventilation to control temperature and moisture. Heat may be added in farrowing houses. Slotted floors are used in confinement houses as a labour-saving approach for handling manure. Fencing and handling feeding and watering equipment are needed for the pig production enterprise. Facilities are cleaned by power washing and disinfecting after all bedding, manure and feed are removed (Gillespie 1997).

Hazards

Injuries from pigs usually occur within or close to farm buildings. Dangerous environments include slippery floors, manure pits, automatic feeding equipment and confinement buildings. Confinement buildings have a manure storage pit that emits gases that, if not ventilated, can kill not only pigs, but workers as well.

Pig behaviour can pose hazards to workers. A sow will attack if her piglets are threatened. Pigs can bite, step on or knock people down. They tend to stay in or return to familiar areas. A pig will try to return to the herd when attempts are made to separate it. Pigs are likely to balk when moved from a dark area into a light area, such as out of a pig house into the daylight. At night, they will resist moving into dark areas (Gillespie 1997).

In a Canadian study of pig farmers, 71% reported chronic back problems. Risk factors include intervertebral disc loading associated with driving and sitting for long periods while operating heavy equipment. This study also identified lifting, bending, twisting, pushing and pulling as risk factors. In addition, more than 35% of these farmers reported chronic knee problems (Holness and Nethercott 1994).

Three types of air exposures pose hazards on pig farms:

1.     dust from feed, animal hair and faecal matter

2.     pesticides used on pigs and other chemicals, such as disinfectants

3.     ammonia, hydrogen sulphide, methane and carbon monoxide from manure storage pits.

Fires in buildings are another potential hazard, as is electricity.

Some zoonotic infections and parasites can be transmitted from the pig to the worker. Common zoonoses associated with pigs include brucellosis and leptospirosis (swineherd’s disease).

Preventive Action

Several safety recommendations have evolved for the safe handling of pigs (Gillespie 1997):

·     Working with small pigs in the same pen as the sow should be avoided.

·     A hurdle or solid panel should be used when handling pigs to avoid bites and being knocked over.

·     A pig can be moved backwards by placing a basket over its head.

·     Children should be kept out of pig pens and not allowed to reach through fences to pet pigs.

·     Because of their herding instincts, it is easier to separate a group of pigs from a herd than a single animal.

·     Pigs can be moved from dark to light areas with the use of artificial light. When pigs are moved at night, such as through chutes or alleys, a light should be placed at the destination.

·     Loading chutes should be level or at not more than a 25-degree angle.

Musculoskeletal injury risk can be decreased by reducing exposure to repetitive trauma (by taking frequent breaks or by varying the kinds of tasks), improving posture, reducing the weight lifted (use co-worker or mechanical assistance) and avoiding rapid, jerking movements.

Dust control techniques include lowering stock density to reduce dust concentration. In addition, automatic feed delivery systems should be enclosed to contain dust. Water misting can be used, but it is ineffective in freezing weather and can contribute to the survival of bioaerosols and increase endotoxin levels. Filters and scrubbers in the air handling system show promise in cleaning dust particles from recirculated air. Respirators are another way to control dust exposures (Feddes and Barber 1994).

Vent pipes should be installed in manure pits to prevent dangerous gases from recirculating into the farm buildings. Electrical power should be maintained to vent fans at the pits. Workers should be trained in the safe use of pesticides and other chemicals, such as disinfectants, used in pig production.

Cleanliness, vaccination, quarantine of sick animals and avoiding exposures are ways to control zoonoses. When treating sick pigs, wear rubber gloves. A person who becomes sick after working with sick pigs should contact a physician (Gillespie 1997).

POULTRY AND EGG PRODUCTION

Steven W. Lenhart

Farm production of birds weighing 18 kg or less includes not only domestic birds such as chickens, turkeys, ducks, geese and guineas, but also game birds produced for hunting, such as partridges, quail, grouse and pheasants. While some of these birds are raised outdoors, the majority of commercial poultry and egg production occurs in specially designed confinement houses or barns. Larger birds weighing between 40 and 140 kg, such as cassowaries, rheas, emus and ostriches, are also raised on farms for their meat, eggs, leather, feathers and fat. However, because of their larger size, most of these birds, which are known collectively as ratites, are usually raised outdoors in fenced-in areas containing shelters.

Chickens and turkeys comprise the majority of poultry produced in the world. US farmers annually produce one-third of the world’s chickens—more than the next six leading chicken-producing countries combined (Brazil, China, Japan, France, the United Kingdom and Spain). Similarly, more than half the world’s turkey production occurs in the United States, followed by France, Italy, the United Kingdom and Germany.

While commercial chicken production occurred in the United States as early as 1880, poultry and egg production was not recognized as a large-scale industry until about 1950. In 1900, a chicken weighed slightly less than a kilogram after 16 weeks. Before the emergence of poultry production as an industry, chickens purchased for eating were seasonal, being most abundant in early summer. Improvements in breeding, feed-to-weight conversion, processing and marketing practices, housing and disease control contributed to the poultry industry’s growth. The availability of artificial vitamin D also made a major contribution. All these improvements resulted in year-round poultry production, shorter production periods per flock and an increase in the number of birds housed together from only a few hundred to several thousand. The production of broilers (7-week-old chickens weighing approximately 2 kg) increased dramatically in the United States, from 143 million chickens in 1940, to 631 million in 1950, to 1.8 billion in 1960 (Nesheim, Austic and Card 1979). US farmers produced approximately 7.6 billion broilers in 1996 (USDA 1997).

Egg production has also seen dramatic growth similar to broiler production. At the beginning of the twentieth century, a laying hen annually produced about 30 eggs, mostly in the spring. Today, the annual average per layer is more than 250 eggs.

Ratite farming primarily consists of the ostrich from Africa, the emu and cassowary from Australia and the rhea from South America. (Figure 70.6 shows a farm flock of ostriches, and figure 70.7  shows a farm flock of emus.) Ratite farming first started in South Africa in the late 1800s in response to a fashion demand for the wing and tail feathers of ostriches. While ostrich plumes no longer decorate hats and clothing, commercial production still occurs not only in South Africa, but also in other African countries such as Namibia, Zimbabwe and Kenya. Ratite farming also occurs in Australia, Germany, Great Britain, Italy, China and the United States. The meat of these birds is gaining popularity because, while it is a red meat with a beefy taste and texture, it has total and saturated fat levels much lower than beef.

Figure 70.6 Part of a commercial flock of 3- to 6-week old ostriches

Roger Holbrook, Postime Ostrich, Guilford, Indiana

When processed at about 12 months of age, each bird will weigh approximately 100 kg,  of which 35 kg is boneless meat. An adult ostrich can weigh as much as 140 kg.

Figure 70.7 Commercial flock of 12-month old emus

Volz Emu Farm, Batesville, Indiana

When processed at about 14 months of age, each bird will weigh between 50  and 65 kilograms, of which approximately 15 kilograms is meat and 15 kilograms  is fat for oil and lotions.

Poultry Confinement Housing

A typical poultry confinement house in the United States is a long (60 to 150 m), narrow (9 to 15 m) single-storey barn with a dirt floor covered with litter (a layer of wood shavings, sphagnum peat or sawdust). Both ends of a confinement house have large doors, and both sides have half-side curtains running the length of the structure. Watering systems (called drinkers) and automatic feeding systems are located close to the floor and run the entire length of a house. Large, 1.2-m diameter propeller fans are also present in a poultry house to keep the birds comfortable. A poultry farmer’s daily tasks include maintaining acceptable environmental conditions for the birds, ensuring the continuous flow of feed and water and collecting and disposing of dead birds.

Watering and feeding systems are raised 2.5 to 3 metres above the floor when a flock reaches its processing age to accommodate catchers, workers who collect the birds for transport to a poultry processing plant. Collecting chickens is usually done by hand. Each member of a crew must bend over or stoop to gather several birds at a time and place them into coops, cages or crates. Each worker will repeat this process several hundred times during a work shift (see figure 70.8). For other types of poultry (e.g, ducks and turkeys), workers herd the birds to a collection area. Turkey catchers wave sticks with red bags tied to them in order to separate several birds at a time from a flock and drive them into a holding pen at the barn's entrance (see figure 70.9).

Figure 70.8 Chicken catchers collecting broilers and placing them in crates  for delivery to a poultry processing plant.

Steven W. Lenhart

Figure 70.9 Turkey catchers separating birds from a flock  and driving them into a holding pen.

Steven W. Lenhart

Poultry confinement houses vary from this general description depending primarily on the type of birds being housed. For example, in commercial egg production, adult hens or layers have traditionally been kept in cages arranged in parallel banks. Caged laying-hen systems will be banned in Sweden in 1999 and replaced by loose laying-hen systems. (A loose laying system is shown in figure 70.10). Another difference between poultry confinement houses is that some do not have litter-covered floors but instead have either slotted or plastic-coated wire floors with manure pits or liquid manure catchment areas under them. In western Europe, poultry confinement houses tend to be smaller than US houses, and they utilize block construction with cement floors for easy litter removal. Western European poultry confinement houses are also decontaminated and floor litter removed after every flock.

Figure 70.10 A loose laying system

Steven W. Lenhart

Health Risks

The health and safety risks of poultry farmers, their family members (including children) and others who work in poultry confinement houses have increased as the poultry industry has grown. Raising a poultry flock requires a farmer to work 7 days a week. Consequently, unlike most occupations, exposures to contaminants occur over several consecutive days, with the period between flocks (as short as 2 days) being the only time of non-exposure to poultry house contaminants. The air of a poultry house can contain gaseous agents such as ammonia from litter, carbon monoxide from poorly ventilated gas-fired heaters and hydrogen sulphide from liquid manure. Also, particles of organic or agricultural dust are aerosolized from poultry house litter. Poultry house litter contains an assortment of contaminants including bird excreta, feathers and dander; feed dust; insects (beetles and flies), mites and their parts; micro-organisms (viral, bacterial and fungal); bacterial endotoxin; and histamine. The air of a poultry house can be very dusty, and for a first-time or occasional visitor, the smell of manure and the pungent odour of ammonia can at times be overwhelming. However, poultry farmers seemingly develop an adaptive tolerance to the smell and to ammonia’s odour.

Because of their inhalation exposures, unprotected poultry workers are at risk of developing respiratory diseases such as allergic rhinitis, bronchitis, asthma, hypersensitivity pneumonitis or allergic alveolitis and organic dust toxic syndrome. Acute and chronic respiratory symptoms experienced by poultry workers include cough, wheezing, excessive mucus secretion, shortness of breath and chest pain and tightness. Pulmonary function testing of poultry workers has provided evidence suggesting not only the risk for chronic obstructive diseases such as chronic bronchitis and asthma, but also restrictive diseases such as chronic hypersensitivity pneumonitis. Common non-respiratory symptoms among poultry workers include eye irritation, nausea, headache and fever. Of approximately 40 zoonotic diseases of agricultural importance, six (Mycobacterium avium infection, erysipeloid, listeriosis, conjunctival Newcastle infection, psittacosis and dermatophytosis) are of concern to poultry workers, although they occur only rarely. Non-zoonotic infectious diseases of concern include candidiasis, staphylococcosis, salmonellosis, aspergillosis, histoplasmosis and cryptococcosis.

There are also health issues affecting poultry workers that are as yet unstudied or poorly understood. For example, poultry farmers and especially chicken catchers develop a skin condition they refer to as galding. This condition has an appearance of a rash or dermatitis and primarily affects a person’s hands, forearms and inner thighs. The ergonomics of poultry catching are also unstudied. Bending to collect several thousand birds every work shift and carrying eight to fifteen chickens, each weighing from 1.8 to 2.3 kg, is physically demanding, but how this work affects a catcher’s back and upper extremities is unknown.

The extent to which the many psychosocial factors associated with farming have affected the lives of poultry farmers and their families is also unknown, but occupational stress is perceived by many poultry farmers as a problem. Another important but unstudied issue is the extent to which the health of farmers’ children is affected as a consequence of work in poultry houses.

Respiratory Health Protection Measures

The best way to protect any worker from exposure to airborne contaminants is with effective engineering controls that capture potential contaminants at their source before they can become airborne. In most industrial environments, airborne contaminants can be reduced to safe levels at their source by the installation of effective engineering control measures. Wearing respirators is the least desirable method for reducing workers’ exposures to airborne contaminants, and respirator use is recommended only when engineering controls are not feasible, or while they are being installed or repaired. Nevertheless, at present, wearing a respirator is still probably the most feasible method available for reducing poultry workers’ exposures to airborne contaminants. The general ventilation systems in poultry houses are not primarily intended to reduce the exposures of poultry workers. Research is going on to develop appropriate ventilation systems to reduce airborne contamination.

Not all respirators provide the same level of protection, and the type of respirator selected for use in a poultry confinement house can vary depending on the age of the birds being raised, age and condition of the litter, drinker type and position of the side curtains (open or closed). All of these are factors affecting airborne agricultural dust and ammonia concentrations. Airborne dust levels are highest during poultry-catching operations, at times to the point that one cannot see from one end of a poultry house to the other. A full-facepiece respirator with high-efficiency filters is recommended as the minimum protection for poultry workers based on bacterial endotoxin measurements made during chicken catching.

When ammonia levels are high, combination or “piggyback” cartridges are available that filter ammonia and particulates. A more expensive powered air-purifying respirator with a full-facepiece and high-efficiency filters may also be appropriate. These devices have the advantage that filtered air is constantly delivered to the wearer’s facepiece, resulting in less breathing resistance. Hooded, powered air-purifying respirators are also available and can be used by bearded workers. Respirators providing less protection than full-facepiece or powered air-purifying types may be adequate for some work situations. However, downgrading the level of protection, such as to a half-mask disposable respirator, is recommended only after environmental measurements and medical monitoring show that the use of a less protective respirator will reduce exposures to safe levels. Repeated exposures of the eyes to poultry dust increase the risk for eye injury and disease. Respirators with full-facepieces and those with hoods have a benefit of also providing eye protection. Poultry workers who choose to wear half-mask respirators should also wear eyecup goggles.

For any respirator to protect its wearer, it must be used in accordance with a complete respiratory-protection programme. However, while poultry farmers experience inhalation exposures for which respirator usage may be beneficial, most of them are not currently prepared to carry out a respiratory protection programme by themselves. This need may be addressed by the development of regional or local respiratory protection programmes in which poultry farmers can participate.

Manure pits should be considered confined spaces. A pit’s atmosphere should be tested if entry is unavoidable, and a pit should be ventilated if it is oxygen-deficient or contains toxic levels of gases or vapours. Safe entry may also require wearing a respirator. In addition, a standby person may be needed to stay in constant visual or speech contact with workers inside a manure pit.

Safety Risks

Safety risks associated with poultry and egg production include unguarded chains, sprockets, winches, belts and pulleys on fans, feeding equipment and other machinery. Scratches, pecks and even bites by the larger birds are also safety hazards. A male ostrich is especially protective of his nest during mating season, and when he feels threatened, he will attempt to kick any intruder. Long toes with sharp nails add to the danger of an ostrich’s powerful kick.

Electrical hazards created by improperly grounded or non-corrosion-resistant equipment or poorly insulated wires in a poultry house can result in electrocution, non-fatal electrical shock or fire. Poultry dust will burn, and poultry farmers tell anecdotes about accumulated dust exploding within gas-fired heaters when the dust was aerosolized during housekeeping chores. Researchers with the US Bureau of Mines have performed explosiveness testing of agricultural dusts. When aerosolized in a 20-litre test chamber and ignited, dust that was collected from the tops of heater cabinets and from window ledges in chicken houses was determined to have a minimum explosible concentration of 170 g/m3. Sieved samples of poultry house litter could not be ignited. By comparison, grain dust evaluated under the same laboratory conditions had a minimum explosible concentration of 100 g/m3.

Safety Measures

Measures can be taken to reduce safety risks associated with poultry and egg production. For protection from moving parts, all machinery should be guarded, and fans should be screened. For tasks involving hand contact with birds, gloves should be worn. High standards of personal hygiene should be maintained, and any injuries, no matter how minor, caused by machinery or birds should be treated immediately to avoid infection. When approaching a ratite, movement toward the bird should be from the side or behind to avoid being kicked. A lockout system should be used when servicing electrical equipment. Poultry farmers should frequently remove settled dust from surfaces, but they should be aware that, on rare occasions, an explosion can result when high concentrations of accumulated dust are aerosolized within an enclosure and ignited.

POULTRY CATCHING, LIVE HAULING AND PROCESSING

The potential for back injuries and respiratory disorders is high for poultry catchers. Many poultry companies in the United States contract out catching birds. Due to the transient nature of the catching crews there are no data indicating injuries or losses. Usually, catching crews are picked up and driven to the grower by company-owned truck. The crew members are either given or sold single use disposable respirators and disposable cotton gloves to protect their hands. Companies should make sure that respiratory protection is worn properly and that their crews have been properly medically evaluated and trained.

Each catch crew member must reach down and grab several struggling birds one after another and may be required to handle multiple birds at once. The birds are placed in a tray or drawer of a multi-bay module. The module holds several trays and is loaded by a company-owned fork-lift onto the bed of the company’s flat bed trailer. The fork-lift operator may either be the company’s truck driver or the contract crew leader. In either case, proper training and operation of the fork-lift must be assured. Speed and coordination are essential among the catching crew.

New methods of catching and loading have been experimented with in the US. One method being tried is a guided gatherer which has arms sweeping inwards guiding the chickens to a vacuum system. Attempts at automation to reduce the physical stresses and potential for respiratory exposure are a long way from success. Only the larger, more efficient poultry companies can afford the capital expenditures necessary to purchase and support such equipment.

A chicken’s normal body temperature is 42.2 °C. Consequently, the mortality rate increases in the winter and in locations where the summers are hot and humid. Both in the summer and winter, the flock must be transported as quickly as possible to be processed. In the summer, prior to processing, trailer loads of modules containing birds must be kept out of the sun and cooled with large fans. Dust, dried faecal matter and chicken feathers are often airborne as a result.

Throughout the entire processing of chicken, rigid sanitation requirements must be met. This means floors must be periodically and often washed down and debris, parts and fat removed. Conveyors and processing equipment must be accessible, washed down and sanitized also. Condensation must not be allowed to accumulate on ceilings and equipment over exposed chicken. It must be wiped down with long-handled sponge mops.

In the majority of the processing plant’s production areas, there is high noise exposure. Unguarded overhead radial blade fans circulate the air in the processing areas. Because of the sanitation requirements, guarded rotating equipment cannot be silenced for noise abatement purposes. An appropriate and well-run hearing conservation programme is necessary. Initial audiograms and annual audiograms should be given and periodic dosimetry should be performed to document exposure. Purchased processing equipment need to have as low an operating noise level as possible.

Particular care needs to be taken in educating and training the workforce. Workers must understand the full implications of exposure to noise and how to wear their hearing protection correctly.

Tony Ashdown

HORSES AND OTHER EQUINES

Lynn Barroby

Horses belong to the equine family, which includes the domesticated African wild ass, also known as the donkey or burro. Historians believe that domestication of the horse began circa 6000 BC and the donkey at least as early as 2600 BC. The mule, bred for work, is a cross between a male donkey (jack or jackass) and a female horse (mare). A mule is unable to reproduce. When a male horse (stallion) is bred with a female donkey (jennet), the offspring, also sterile, is called a hinny. Horses and donkeys have also been crossed with another equine, the zebra, and the offspring are collectively called zebroids. Zebroids are also sterile and of little economic importance (Caras 1996).

Processes

Of the 10 million horses in the United States, about 75% are used for personal pleasure riding. Other uses include racing, ranching, breeding and commercial riding. The horse has become a performer in racing, jumping, rodeo and many more events.

The three main horse enterprises are breeding, training and boarding stables. Horse breeding farms breed mares and sell the offspring. Some farms specialize in training horses for show or racing. Boarding stables feed and care for horses for customers who have no facilities to house their horses. All three of these enterprises are labour intensive.

Horse breeding is an increasingly scientific process. Pasture breeding was typical, but now it is generally controlled within a breeding barn or corral. Although artificial insemination is used, it is more common that mares are brought to the stallion for breeding. The mare is checked by a veterinarian and, during breeding, trained workers handle the stallion and the mare.

After giving birth, the mare nurses the foal until it is from 4 to 7 months of age; after weaning, the foal is separated from the mare. Some colts not meant for breeding may be castrated (gelded) as early as 10 months of age.

When a racehorse becomes a two-year-old, professional trainers and riders start breaking it to ride. This involves a gradual process of getting the horse used to human touch, being saddled and bridled, and finally mounted. Horses that race with carts and heavy draught horses are broke to drive at about two years of age, and ranch horses are broke at closer to three years old, sometimes using the rougher method of bucking a horse out.

In horse racing, the groom leads the horse to the saddling paddock, a trainer and a valet saddle it, and a jockey mounts it. The horse is led by a pony horse and rider, warmed up and loaded into the starting gate. Racehorses can become excited, and the noise of a race can further excite and frighten the horse. The groom takes a winning horse to a drug test barn for blood and urine samples. The groom must then cool the horse down with a bath, walking and sipping water.

A groom cares for the performance horse and is responsible for brushing and bathing it, saddling it for the exercise rider, applying any protective bandages or boots to its legs, cleaning the stall and bedding down straw, shavings, peat moss, peanut skins, shredded newspaper or even rice hulls. The groom or a “hot” walker walks the horse; sometimes a mechanical walker is used. The groom feeds the horse hay, grain and water, rakes and sweeps, washes the horse’s laundry and carts manure away in a wheelbarrow. The groom holds the horse for others such as the veterinarian or farrier (farrier work is traditionally done by a blacksmith). All horses require parasite control, hoof care and teeth-filing.

Performance horses are typically stabled and given daily exercise. However, young stock and pleasure riding horses are generally stabled at night and released during the day, while others are kept outdoors in paddocks or pastures with sheds for shelter. Race horses in training are fed three or four times a day, while show horses, other performance horses, and breeding stock are fed twice a day. Range or ranch stock are fed once a day, depending on the forage present.

Horses travel for many reasons: shows, races, for breeding or to riding trails. Most are shipped by truck or trailer; however, some travel by rail or plane to major events.

Hazards and Precautions

Several hazards are associated with working around horses. A groom has a physically demanding job with a lot of forking of manure, moving 25 to 50 kg hay and straw bales and handling active horses. Startled or threatened horses may kick; thus, workers should avoid walking behind a horse. A frightened horse may jump and step on a worker’s foot; this can also occur accidentally. Various restraints are available to handle fractious horses, such as a chain over the nose or a lip chain. Stress on horses due to shipping may cause balking and injuries to the horses and handlers.

The groom is potentially exposed to hay and grain dust, dust from bedding, moulds, horse dander and ammonia from the urine. Wearing a respirator can provide protection. Grooms do a lot of leg work on the horses, sometimes using liniments containing hazardous chemicals. Gloves are recommended. Some leather-tack care products can contain hazardous solvents, requiring ventilation and skin protection. Cuts can lead to serious infections such as tetanus or septicaemia. Tetanus shots should be maintained current, especially because of exposure to manure.

A farrier is exposed to injury when shoeing a horse. The groom’s job is to hold the horse to keep it from kicking the farrier or pulling its foot in a way that could strain the farrier’s back or cut the farrier with the horseshoe and nails.

In the drug test barn, the test person is enclosed in a stall with a loose, excited and unfamiliar horse. He or she holds a stick (with a cup for urine) that may frighten the horse.

When riding horses, it is important to wear a good pair of boots and a helmet. Any mounted person needs a protective vest for racing, jumping, rodeo broncs, and ponying or exercising racehorses. There is always a danger of being bucked off or of a horse stumbling and falling.

Studs can be unpredictable, very strong and can bite or kick viciously. Brood mares are very defensive of their foals and can fight if threatened. Studs are kept individually in high-fenced paddocks, while other breeding stock are kept in groups with their own pecking order. Horses trying to move away from a boss horse or a group of yearlings at play can run over anyone who gets in the way. Foals, weanlings, yearlings and two-year-olds will bite and nip.

Some drugs (e.g., hormones) used in breeding are given orally and can be harmful to humans. Wearing gloves is recommended. Needle-stick injuries are another hazard. Good restraints, including stocks, can be used to control the animal during administration of medication. Topical sprays and automatic stable spray systems to control flies can easily be overused in horse rearing. These insecticides should be used in moderation, and warning labels should be read and recommendations followed.

There are a variety of zoonoses that can be passed from horses to humans, especially skin infections from contact with infected secretions. Horse bites can be a cause of some bacterial infections. See table 70.19  for a list of zoonoses associated with horses.

Table 70.19 Zoonoses associated with horses

Viral diseases

  • Rabies (very low occurrence)
  • Eastern, western and some subtypes of  Venezuelan equine encephalomyelitis
  • Vesicular stomatitis
  • Equine influenza
  • Equine morbillvirus disease (first documented in Australia in 1994)

Fungus infections

  • Ringworm (dermatomycoses)

Parasitic zoonoses

  • Trichinosis (large outbreaks in France and Italy in the 1970s and 1980s)
  • Hydatid disease (echinoccosis) (very rare)

Bacterial diseases

  • Salmonellosis
  • Glanders (now very rare, restricted to Middle East and Asia)
  • Brucellosis (rare)
  • Anthrax
  • Leptospirosis (relatively rare, direct human contamination not definitively proven)
  • Melioidosis (outbreaks in France in the 1970s and 1980s; direct transmission not reported)
  • Tuberculosis (very rare)
  • Pasteurellosis
  • Actinobacillus lignieresii, A., A. suis (suspected in Lyme disease transmission, Belgium)

ELEPHANTS

The largest draught animal is the elephant, but its role is slowly becoming one of tradition rather than necessity. Two decades ago, 4,000 Asian elephants were used for logging in Thailand, but the forests there have been clear-cut and mechanization has displaced the elephant. However, they are still used in Myanmar, where elephant logging is prevalent. Logging companies frequently lease working elephants from their owners, who are typically urban businessmen.

The elephant handler (or trainer) is called an oozie in Myanmar and a mahout in India and Sri Lanka. The trainer mounts a saddle—a thick pad of leaves and bark—on the elephant’s back to protect its sensitive spine from the dragging gear, or tack, used in pulling logs. The trainer sits on the elephant’s neck as it uses its trunk, tusks, feet, mouth and forehead to accomplish its daily chores. A well-trained elephant in logging work will respond to more than 30 vocal commands and 90 pressure points on its body from a skilled handler. They work until 2:45 every afternoon, then the oozie scrubs the elephant in water with coconut halves for up to an hour. The oozie then feeds the elephant salted, cooked rice and hobbles and releases it to feed in the forest at night. At about 4:00 a.m., the oozie locates the elephant by unique tones of a bell that is attached to the elephant (Schmidt 1997).

Elephant bulls are rarely held in captivity, and cows are traditionally released to be bred in the wild. Artificial insemination is also used to breed elephants. Bull elephants donate semen to an elephant-sized artificial cow. It is impossible to observe visually the cow in oestrus (three times per year), so weekly samples of blood are taken for progesterone analysis. When a cow is in oestrus, she is bred by injecting semen into her vagina with a long, flexible pneumatic insemination tube.

Several hazards are associated with elephant handling; they arise from elephants’ size, the massive objects of their work and their behaviour. Mounting the tack on the elephant and manipulating logging gear exposes the handler to injury hazards. In addition, the handler is exposed to falls from the elephant’s neck. The potential for injury is aggravated by the logging operations, which include carrying, pushing, pulling and stacking; teak logs can weigh as much as 1,360 kg. The elephant’s behaviour may be unpredictable and cause injury to its handler. Captive bulls are very dangerous and are difficult to contain. Breeding bulls are particularly dangerous. A working bull elephant in Sri Lanka has been reported to have killed nine mahouts. He was retained after each death, however, because of his value to his owners (Schmidt 1997).

Some elephants will respond only to their trainer. The principal method for controlling unpredictable elephants is to allow only their oozie to handle them. Elephants are creatures of habit, so trainers should maintain a daily routine. The afternoon scrubbing by the trainer has been found to be critical in establishing a bond with the elephant. Maintaining the trainer’s dominance is another safeguard against unsafe elephant behaviour.

The swimmers who carry blood samples to a laboratory for progesterone analysis are exposed to a particularly dangerous task: they swim across rivers during the monsoon season. This drowning hazard can be corrected by providing laboratory services near the working elephants.

Melvin L. Myers

DRAUGHT ANIMALS IN ASIA

D.D. Joshi

Livestock contributes significantly to the life of small farmers, nomads and foresters all over the world and increases their productivity, income, employment and nutrition. This contribution is expected to rise. The world population will rise from its present 4.8–5.4 billion people to at least 10 billion in the next 100 years. The population of Asia can be expected to double over that same period. The demand for food will rise even more as the standard of living also rises. Along with this will be a rise in the need for draught power to produce the increased food required. According to Ramaswami and Narasimhan (1982), 2 billion people in the developing countries depend on draught animal power for farming and rural transportation. Draught power is critically short at the time of crop planting and is insufficient for other purposes throughout the year. Draught power will remain a major source of energy in agriculture into the foreseeable future, and the lack of draught power in some places may be the primary constraint to increasing crop production.

Animal draught power was the first supplement to human energy inputs in agriculture. Mechanized power has been used in agriculture only in the last century or so. In Asia, a greater proportion of farmers depend on animals for draught power than in any other parts of the world. A large proportion of these animals belong to farmers who have limited resources and cultivate small areas of land. In most parts of Asia, animal power is supplied by bullocks, buffalo and camels. Bullocks will continue to be the common source of farm power, mainly because they are adequate and live on waste residues. Elephants are also used in some places.

Production

In Asian countries, there are three main sources of power used in agriculture: human, mechanical and animal. Human beings provide the main source of power in developing countries for hoeing, weeding, rice transplanting, seed broadcasting and harvesting of crops. Mechanical power with its versatility is used for practically all the field operations, and the intensity of usage varies considerably from one developing country to another (Khan 1983). Animal power is generally used for tillage operations, haulage and operation of some water-lifting devices. A draught cow is a multipurpose farm animal, providing power, milk, dung, calves and meat. Normal draught power of various animals is presented in table 70.20 .

Table 70.20 Normal draught power of various animals

Animals

Weight (kg)

Approx. draught (kg)

Average speed of work (m/sec)

Power developed (h.p.)

Light horses

400–700

60–80

1.0

1.00

Bullocks

500–900

60–80

0.6–0.85

0.75

Buffaloes

400–900

50–80

0.8–0.90

0.75

Cows

400–600

50–60

0.7

0.45

Mules

350–500

50–60

0.9–1.0

0.70

Donkeys

200–300

30–40

0.7

0.35

Source: FAO 1966.

To have better draught animal power the following aspects should be considered:

For landless people to repay a loan for purchase of bullocks, feed them, and earn sufficient income to meet everyday costs, they must be able to work their animals for six hours per day.

·     Draught animal nutrition. Animal nutrition is a principal factor in increasing the productivity of draught animal power. This is possible only if the necessary feed is available. In some areas, more effort is made to ensure the best use of available resources, such as treating straw with alkali (molasses urea block (MUB)) to improve its nutrient availability. As draught power availability is presently limiting the production of staple crops (there is an estimated 37% deficiency in draught requirements at the time of harvest), a primary objective is to produce draught animals and improve the efficiency of draught power. The opportunity to use improved nutritional technology (e.g., MUB) may assist draught power development through improved animal work capacity and reproduction rates in the female herd as well as better growth of young animals, which will lead to larger body size.

·     Breeding and selection. Culling of local unproductive breed bulls and selection of the best local bull is necessary. Draught animals are currently selected according to their conformation, temperament and health; however, farmers often must rely on what is available locally.

Some crossbreds show a significant increase not only in milk and meat producing capability, but also in draught power. In India, Pakistan and Australia there have been tremendous efforts made in cross-breeding buffalo, cattle, horses (to produce mules) and, in some places, camels. This has produced very encouraging results. In many other Asian countries, especially developing countries, this research work for improving draught power as well as milk and meat production is very much needed.

·     Equipment. Most farm equipment is old and unproductive. Much of the equipment that is used in conjunction with draught animals (harnesses, cultivation tools and carts) is of traditional type, the design of which has not changed for hundreds of years. In addition, farm implements are often badly designed and achieve low work output.

·     Health. The stress of working may upset the balance which often exists between healthy animals and parasites.

Management

The daily feeding of draught animals varies according to work season. Both draught cattle and buffalo are fed in confinement (year-round) through a cut and carry system, with little or no grazing. Rice straw is fed all year long, depending on farmer preference, at either a measured rate of 8 to 10 kg per day or as necessary. Other crop residues such as rice hulls, pulse straw and cane tops are fed when available. In addition to these crop residues, cut or grazed green grass from roadsides and embankments is fed during the rainy season (April into November) at the rate of 5 to 7 kg/day and may be increased during times of heavy work to 10 kg/day.

Draught animal feed is usually supplemented with small amounts of by-product concentrates such as brans, oil cakes, pulses, rice hulls and molasses. The predominant means of feeding concentrates to draught animals is in a liquid form with all of the ingredients mixed together. The types and amounts of ingredients vary according to the daily workload of the animal, the geographical area, farmer preference and capability. Increased amounts of concentrates are fed during the heavy work seasons, and they are reduced during the monsoon season, when the workload is light.

Animal feed ingredients are also chosen by farmers based on availability, price, and their perception and understanding of its feeding value. For example, during the work season from November to June, daily rations may be: 200 g of mustard seed oil cake along with 100 g (dry weight) of boiled rice; 3/4 g of mustard seed oil cake, 100 g boiled rice and 3/4 g of molasses; or 2 kg total of equal parts sesame oil cake, rice polish, wheat bran and boiled rice, along with salt. On actual workdays during this period (163 days), animals are fed an extra 50% of these same rations. If animals are fed any concentrates at all during the non-working season, the rate ranges from 1/4 to 1/2 kg.

Draught Power in Australia

The Australian continent was first colonized by Europeans in 1788. Cattle were introduced with the first ships, but escaped into the surrounding forest. During those days ploughing and other land preparation was done with the heavy bullock plough, and light cultivation either with bullocks or horses. The bullock cart became the standard means of land transport in Australia and remained so until road building and railway construction began and became more widespread following the gold rushes from 1851 onwards.

In Australia other draught animals include the camel and the donkey. Although mules were used, they never became popular in Australia (Auty 1983).

Draught Power in Bangladesh

In Bangladesh livestock play a vital role in the economy, providing both draught power and milk and contributing up to 6.5% of the gross domestic product (GDP) (Khan 1983). Out of the 22 million head of cattle, 90% are used for draught power and transportation. Of this total, 8.2 million are dual purpose, supplying both draught power and dairy products, such as milk and meat (although in minimal amounts) for household consumption and trade. Adding energy value from draught power and dung (fertilizer and fuel), livestock contribute an estimated 11.3% to the GDP.

It has been observed that some cows are used for draught purposes, despite problems with fertility and health complications, which result in lower milk production and fewer calvings per lifetime. While cows are not usually worked during lactation, they contribute significantly to the annual supply of draught power in Bangladesh: 2.14 million (31%) adult female cattle and 60,000 (47%) adult buffalo cows supply animal power (Robertson et al. 1994). When combined with the male workforce, 76% of all adult cattle (11.2 million) and 85 to 90% of all adult buffalo (0.41 million) are used for draught purposes (Khan 1983).

There is no aggregate shortage of draught animals. Rather, the shortfall is based on the quality of draught power available, since malnourished animals are largely unproductive (Orlic and Leng 1992).

There are various breeds of cattle used for draught purposes, including pure deshi cattle and deshi cattle crossed with Sahiwal, Haryana and Red Sindhi cattle and Manipuri, Nili-Ravi and Murrah breeds of buffalo. Deshi bullocks weigh an average of 225 kg, crossbreds are slightly heavier at 275 kg and buffalo weigh an average of 400 kg. Bulls, cows, heifers and bullocks all provide animal power, but bullocks constitute the main workforce.

In Bangladesh, land preparation employs the highest percentage of draught animals. Research workers recommend that land be ploughed six to seven times prior to sowing. However, due to the shortage of draught power, many producers plough only four to five times in preparation for each crop. All ploughs in Bangladesh require two animals. Two bullocks can plough 1 acre in 2.75 (at 6 hours each day) (Orlic and Leng 1992; Robertson et al. 1994).

Draught Power in China

China has a long history of buffalo raising. The animals were used for farming as early as 2,500 years ago. Buffalo have a larger body size than the native cattle. Farmers prefer to use buffalo for farm work because of their great draught power, long working life and docile temperament. One buffalo can provide draught power for the production of 7,500 to 12,500 kg of rice (Yang 1995). Most of them are kept by small-scale farmers for draught purpose. The imported dairy buffalo, Murrah and Nili/Ravi, and crossbreds with these two breeds, are mainly raised on state farms and in research institutes. For centuries, buffalo have been reared mainly for draught purposes. The animals were slaughtered for meat only when they become old or disabled. Milking of buffalo was rare. After generations of selection and breeding, the buffalo have become extremely suitable for working, with deep and strong chests, strong legs, large hoofs and a docile temperament.

In China, buffalo are mainly used for paddy land and for field haulage. They are also employed in raising water, pudding clay for bricks, milling and pressing the juice from sugarcane. The extent of such use is declining due to mechanization. Training of buffalo usually starts at the age of two years. They begin to work a year later. Their working life is longer than that of cattle, usually more than 17 years. It is possible to see buffalo more than 25 years old still working in the fields. They work 90 to 120 days per year in the rice-growing area, with intensive work in the spring and autumn, when they work as long as 7 to 8 hours per day. The working capability varies widely with size, age and sex of the animal. The draught power reaches its maximum between the age of five and 12 years, remains high from 13 to 15 and begins to decline from 16 years. Most of the buffalo bulls are castrated (Yang 1995).

The Shanghai buffalo, one of the largest in China, has an excellent working capability. Working for 8 hours a day, one animal can plough 0.27 to 0.4 hectare of paddy land or 0.4 to 0.53 hectare of non-irrigated land (maximum 0.67 hectare). A load of 800 to 1,000 kg on a wooden-wheeled, bearingless vehicle can be drawn by a buffalo over 24 km within a working day. A buffalo can raise enough water to irrigate 0.73 hectares of paddy land in 4 hours.

In some sugar-producing areas, buffalo are used to draw stone rollers for sugar cane pressing. Six buffalo working in shifts can press 7,500 to 9,000 kg of sugar cane, requiring 15 to 20 minutes for every 1,000 kg.

Draught Power in India

According to Ramaswami and Narasimhan (1982) 70 million bullocks and 8 million buffalo generate about 30,000 million watts of power, assuming the Indian Council of Agricultural Research (ICAR) average of 0.5 hp output per animal. To generate, transmit and distribute this power at the same multitudinous points of application would call for an investment of 3,000,000 million rupees. It has also been estimated that an investment of 30,000 million rupees has gone into the Indian bullock cart system as against 45,000 million rupees in railways.

The Ministry of Shipping and Transport estimated that 11,700 to 15,000 million tonnes of freight in the urban areas is carried by cart each year, as against the railway haulage of 200,000 million tonnes. In the rural areas, where railroad service is not available, animal-drawn vehicles carry approximately 3,000 million tonnes of freight (Gorhe 1983).

Draught Power in Nepal

In Nepal, bullocks and male buffalo are the main source of draught power for tilling the fields. They are also used for carting, crushing sugar cane and oil seeds and for tracting loads. Due to the topographic nature of the country as well as the high cost of fuel, there is little opportunity for farm mechanization. Therefore, the demand for draught animal power in the country is high (Joshi 1983).

In wheat production, the contribution of bullocks in terms of labour days is 42% in ploughing, 3% in transplanting and 55% in threshing. In paddy production, it is 63% in ploughing, 9% in transplanting and 28% in threshing (Joshi 1983; Stem, Joshi and Orlic 1995).

Depending on the task, draught animals are generally worked a consistent number of hours each day and for a predetermined number of consecutive days before being allowed to rest. For instance, a full day of ploughing averages 6 hours for a bullock, and the average workday for a cow ranges from 4 to 5 hours per day. Animals used for ploughing follow a pattern of 6 to 8 consecutive days of work, followed by 2 days of rest. In the case of threshing, cows or lighter-weight animals usually work for 6 to 8 hours each day. The length and pattern of use for threshing and transport varies according to need. A bullock in full-time ploughing (maximum heavy labour) typically works for 163 days per year.

Draught Power in Sri Lanka

The total cattle population in Sri Lanka is estimated at 1.3 million. Various breeds are used as draught animals. Cattle breeds are used for draught purposes such as transport and ploughing of both wet and dry fields, as well as in farm operations. Indigenous animals have been used popularly in road transport for several decades. Crosses of Indian breeds with the indigenous cattle have resulted in larger animals that are used extensively for road transport. Out of a total buffalo population of 562,000, the number available in the work age range of three to 12 years is estimated at 200,000 males and 92,000 females.

Potential Hazards and Their Control

Other articles in this chapter address hazards and preventive actions for the draught animals discussed in this article. General information on animal behaviour and a checklist for livestock rearing safety practices are found in boxes on these subjects in the chapter "Animal husbandry". Horses are addressed in the article "Horses and other equines". Cattle (and by close association, bullocks and buffalo) are addressed in the article "Cattle, sheep and goats". "Bull raising"” also offers pertinent information on potential hazards and their control.

BULL RAISING

David L. Hard

While the term bull refers to the male of several species of livestock (elephant, water buffalo and cattle) this article will deal specifically with the cattle industry. The National Traumatic Occupational Fatalities (NTOF) surveillance system in the United States, based on death certificates and maintained by the National Institute for Occupational Safety and Health (NIOSH), identified 199 fatalities from 1980 to 1992 associated with the agricultural production industry and inflicted by livestock. Of these, about 46% (92) were directly attributed to beef and dairy bull handling.

Cattle raisers have for centuries used castration of male animals as a means of producing docile males. Castrated males are generally passive, indicating that hormones (largely testosterone) are related to aggressive behaviour. Some cultures place high value on the fighting character of bulls, which is utilized in sports and social events. In this case, certain bloodlines are bred to maintain and enhance these fighting characteristics. In the United States, demand has increased for bulls used in rodeos as these entertainment events have increased in popularity. In Spain, Portugal, parts of France, Mexico and parts of South America, bullfighting has been popular for centuries. (See the article “Bullfighting and rodeos” in the chapter Entertainment and the arts.)

The cattle industry can be divided into two major categories—dairy and beef—with some dual-purpose breeds. Most commercial beef operations purchase bulls from pure-bred producers, while dairy operations have moved more toward artificial insemination (AI). Thus, the pure-bred producer generally raises the bulls and then sells them when they are of breeding age (2 to 3 years of age). There are three systems of mating currently used in the cattle industry. Pasture mating allows bull to run with the herd and breed cows as they come into oestrus (heat). This can be for the entire year (historically) or for a specific breeding season. If specific breeding seasons are utilized, this necessitates separating the bull from the herd for periods of time. Hand mating keeps the bull isolated from the cows, except when a cow in oestrus is brought to the bull for mating. Generally, only a single mating is allowed, with the cow being removed after service. Finally, AI is the process of using proven sires, through the use of frozen semen, to be bred to many cows by AI technicians or the producer. This has the advantage of not having a bull at the ranch, which is a reduction of risk for the producer. However, there is still potential for human-animal interaction at the point of semen collection.

When a bull is removed from the herd for hand mating or kept isolated from the herd to establish a breeding season, he may become aggressive when he detects a cow in oestrus. Since he cannot respond naturally through mating, this can lead to the “mean bull” complex, which is an example of abnormal behaviour in bulls. Typical antagonistic or combative behaviour of bulls includes pawing the ground and bellowing. Furthermore, disposition often deteriorates with age. Old breeding stock can be cantankerous, deceptive, unpredictable and large enough to be dangerous.

Facilities

To ensure movement of animals through facilities, chutes should be curved so that the end cannot be seen when first entering, and the corral should be designed with a gap to the left or right so that animals do not sense that they are trapped. Putting rubber bumpers on metal items which create a loud noise when they close can help lessen the noise and reduce stress to the animal. Ideally, facilities should maximize the reduction of hazards due to physical contact between the bull and humans through use of barriers, overhead walkways and gates that can be manipulated from outside the enclosure. Animals are less likely to balk in chutes built with solid walls instead of fencing materials, since they would not be distracted by movement outside the chutes. Alleyways and chutes should be large enough so the animals can move through them, but not so wide they can turn around.

Guidelines for Handling

Male animals should be considered potentially dangerous at all times. When bulls are kept for breeding, injuries can be avoided by having adequate bull-confinement and restraint facilities. Extreme caution should be practised when handling male animals. Bulls may not purposefully hurt people, but their size and bulk make them potentially dangerous. All pens, chutes, gates, fences and loading ramps should be strong and work properly. Proper equipment and facilities are necessary to assure safety. Ideally, when working with bulls, having the handler physically separated from contact with the bull (outside the area and protected by chutes, walls, barriers and so on) greatly reduces the risk of injury. When handlers are with the animal, escape passages should be provided to allow handlers to escape from animals in an emergency. Animals should not be prodded when they have no place to go. Handlers should stay clear of animals that are frightened or “spooked” and be extra careful around strange animals. Solid wall chutes, instead of fencing, will lower the number of animals that balk in the chute. Since bulls see colours as different shades of black and white, facilities should be painted all in the same colour. Properly designed treatment stalls and appropriate animal-restraint equipment and facilities can reduce injuries during animal examination, medication, hoof trimming, dehorning and hand mating.

People who work with animals recognize that animals can communicate despite being unable to speak. Handlers should be sensitive to warnings such as raised or pinned ears, raised tail, pawing the ground and bellowing. General information and guidelines for working with bulls are provided in the animal behaviour in this chapter.

Zoonoses

Handlers should also be concerned with zoonotic diseases. A livestock handler can contract zoonotic illnesses by handling an infected animal or animal products (hides), ingesting animal products (milk, undercooked meat) and disposing of infected tissues. Leptospirosis, rabies, brucellosis (undulant fever in humans), salmonellosis and ringworm are especially important. Tuberculosis, anthrax, Q fever and tularaemia are other illness that should be of concern. To reduce exposure to disease, basic hygiene and sanitation practices should be used, which include prompt treatment or proper disposal of infected animals, adequate disposal of infected tissues, proper cleaning of contaminated sites and proper use of personal protective equipment.

The most sanitary method of carcass disposal is burning it at the site of death, to avoid contamination of the surrounding ground. A hole of appropriate size should be dug, flammable materials of sufficient quantity placed inside and the carcass placed on top in order that it can be consumed in its entirety. However, the most common method of carcass disposal is burial. In this procedure, the carcass should be buried at least 4 feet deep and covered with quicklime in soil that is not susceptible to contamination by drainage and away from flowing streams.

PET, FURBEARER AND LABORATORY ANIMAL PRODUCTION

Christian E. Newcomer

Processes

Institutional animal programmes involve four major processes:

1.     receipt, quarantine and separation of animals

2.     separation of species or animals for individual projects when necessary

3.     housing, care and sanitation

4.     storage.

Husbandry tasks include feeding, watering, providing bedding, maintaining sanitation, disposing of waste including carcasses, controlling pests and veterinarian care. Materials handling is significant in most of these tasks, which include moving cages, feed, pharmaceuticals, biologics and other supplies. Handling and manipulating animals is also fundamental to this work. Sanitation involves changing bedding, cleaning and disinfecting, and cage washing is a significant sanitation task.

Institutional animal facilities include cages, hutches, pens or stalls within a room, barn or outdoor habitat. Adequate space, temperature, humidity, food and water, illumination, noise control and ventilation are provided in a modern facility. The facility is designed for the type of animal that is confined. Animals that are typically confined in institutional settings include group-housed rodents (mice, rats, hamsters and guinea pigs), rabbits, cats, dogs, mink, non-human primates (monkeys, baboons and apes), birds (pigeons, quail and chickens) and farm animals (sheep and goats, swine, cattle, horses and ponies).

Hazards and Precautions

Persons involved with the production, care and handling of pet, furbearer and laboratory animals are potentially exposed to a variety of biological, physical and chemical hazards that can be controlled effectively through available risk reduction practices. The biological hazards intrinsic to the various animal species of concern to personnel include: bites and scratches; highly sensitizing allergens in dander, serum, tissues, urine or salivary secretions; and a wide variety of zoonotic agents. Although the biological hazards are more diverse and potentially more devastating in the work environments supporting these types of animals, the physical and chemical hazards generally are more pervasive, as reflected by their contribution to illness and injury in the workplace.

Personnel involved in the care and production of pet, furbearer or laboratory animals should receive appropriate training in handling techniques and behaviour of the animal species in question, because incorrect handling of an intractable animal frequently is a precipitating cause of a bite or scratch. Such injuries can become contaminated with micro-organisms from the animal’s rich oral and skin microflora or the environment, necessitating immediate wound disinfection and prompt and aggressive antimicrobial therapy and tetanus prophylaxis to avert the serious complications of wound infection and disfigurement. Personnel should appreciate that some zoonotic bite infections can produce generalized disease and even death; examples of the former include cat scratch fever, rat bite fever and human orf infection; examples of the latter include rabies, B virus and hantavirus infection.

Due to these extraordinary risks, wire-mesh, bite-proof gloves can be beneficial in some circumstances, and the chemical restraint of animals to facilitate safe handling is sometimes warranted. Personnel also can contract zoonoses through the inhalation of infectious aerosols, contact of the organisms with the skin or mucous membranes, ingestion of infectious materials or transmission by specific fleas, ticks or mites associated with the animals.

All types of zoonotic agents occur within pet, furbearer and laboratory animals, including viruses, bacteria, fungi and internal and external parasites. Some examples of zoonoses include: giardiasis and campylobacterosis from pets; anthrax, tularaemia and ringworm from furbearers; and lymphocytic choriomeningitis, hantavirus and dwarf tapeworm infestation from the laboratory rodent. The distribution of zoonotic agents varies widely according to host animal species, location and isolation from other disease reservoirs, housing and husbandry methods, and history and intensity of veterinary care. For example, some of the commercially produced laboratory animal populations have undergone extensive disease eradication programmes and been maintained subsequently under strict quality control conditions precluding the reintroduction of diseases. However, comparable measures have not been applicable universally in the various settings for pet, furbearer and laboratory animal maintenance and production, enabling the persistence of zoonoses in some circumstances.

Allergic reactions, ranging from ocular and nasal irritation and drainage to asthma or manifesting on the skin as contact urticaria (“hives”), are common in individuals who work with laboratory rodents, rabbits, cats and other animal species. An estimated 10 to 30% of individuals working with these animal species eventually develop allergic reactions, and persons with pre-existing allergic disease from other agents are at higher risk and have an increased incidence of asthma. In rare circumstances, such as a massive exposure to the inciting allergen through an animal bite, susceptible persons can develop anaphylaxis, a potentially life-threatening generalized allergic reaction.

Good personal hygiene practices should be observed by personnel to reduce their likelihood of exposure to zoonoses and allergens during work with animals or animal by-products. These include the use of dedicated work clothing, the availability and use of hand washing and shower facilities and separation of personnel areas from animal housing areas. Work clothing or protective outer garments covering the skin should be worn to prevent exposure to bites, scratches and hazardous microbes and allergens. Personal protective equipment, such as impervious gloves, safety glasses, goggles or other eye protection, and respiratory protection devices (e.g., particle masks, respirators or positive air pressure respirators) appropriate to the potential hazards and the individual’s vulnerability, should be provided and worn to promote safe work conditions. Engineering controls and equipment design also can effectively reduce the exposure of personnel to hazardous allergens and zoonoses through directional air flow and the use of isolation caging systems that partition the workers’ and animals’ environments.

Personnel also encounter significant physical and chemical hazards during animal care. Routine husbandry tasks involve moving or lifting heavy equipment and supplies, and performing repetitive tasks, affording personnel the ubiquitous opportunity to develop cuts and crush injuries, muscular strains and repetitive motion injuries. Work practice redesign, specialized equipment and personnel training in safe work practices can be used to curb these untoward outcomes. Equipment and facility sanitation frequently relies on machinery operating on live steam or extremely hot water, placing personnel at risk of severe thermal injury. The correct design, maintenance and utilization of these devices should be assured to prevent personnel injury and facilitate heat dissipation to provide a comfortable work environment. Personnel who work around large equipment, as well as around rambunctious dog or non-human primate populations, may be exposed to extremely high noise levels, necessitating the use of hearing protection. The various chemicals used for cage and facility sanitation, pest control within the animal facility and external parasite control on animals should be reviewed carefully with personnel to ensure their strict adherence to practices instituted to minimize exposure to these potentially irritating, corrosive or toxic substances.

FISH FARMING AND AQUACULTURE

George A. Conway and Ray RaLonde

Background

Rearing marine organisms for food has been a widespread practice since ancient times. However, large-scale farming of molluscs, crustaceans and bony fishes has rapidly gained momentum since the early 1980s, with 20% of the world’s seafood harvest now farmed; this is projected to increase to 25% by 2000 (Douglas 1995; Crowley 1995). Expansion of world markets contemporaneous with depletion of wild stocks has resulted in very rapid growth of this industry.

Land-based aquaculture takes place in tanks and ponds, while water-based culture systems generally employ screened cages or moored net pens of widely varying designs (Kuo and Beveridge 1990) in salt water (mariculture) or fresh rivers.

Aquaculture is performed as either an extensive or intensive practice. Extensive aquaculture entails some form of environmental enhancement for naturally produced species of fish, shellfish or aquatic plants. An example of such a practice would be laying down oyster shells to be used as attachment substrate for juvenile oysters. Intensive aquaculture incorporates more complex technology and capital investment in the culture of aquatic organisms. A salmon hatchery that uses concrete tanks supplied with water via some delivery system is an example. Intensive aquaculture also requires greater allocation of labour in the operation.

The process of intensive aquaculture includes the acquisition of broodstock adults used for production of gametes, gamete collection and fertilization, incubation of eggs and juvenile rearing; it may include rearing of adults to market size or release of the organism into the environment. Herein lies the difference between farming and enhancement aquaculture. Farming means rearing the organism to market size, generally in an enclosed system. Aquaculture for enhancement requires the release of the organism into the natural environment to be harvested at a later date. The essential role of enhancement is to produce a specific organism as a supplement to natural production, not as a replacement. Aquaculture can also be in the form of mitigation for loss of natural production caused by a natural or human-made event—for example, construction of a salmon hatchery to replace lost natural production caused by the damming of a stream for hydroelectric power production.

Aquaculture can occur in land-based facilities, on-bottom marine and freshwater environments and floating structures. Floating net pens are used for fish farming, and cages suspended from raft or buoy flotation are commonly used for shellfish culture.

Land-based operations require the construction of dams and/or excavation of holes for ponds and raceways for water flushing. Mariculture can involve the construction and maintenance of complex structures in harsh environments. Handling of smolt (for bony fishes) or tiny invertebrates, feed, chemical treatments for water and the animals being raised and wastes have all evolved into highly specialized activities as the industry has developed.

Hazards and Controls

Injuries

Fish farming operations afford many injury risks, combining some of those common to all modern agriculture operations (e.g., entanglement in large machinery, hearing loss from prolonged exposure to loud engines) with some hazards unique to these operations. Slips and falls can have particularly bad outcomes if they occur near raceways or pens, as there are the dual added risks of drowning and biological or chemical contamination from polluted water.

Severe lacerations and even amputations may take place during roe-stripping, fish butchering and mollusc shelling and can be prevented by the use of guards, protective gloves and equipment designed specifically for each task. Lacerations contaminated by fish slime and blood can cause serious local and even systemic infections (“fish poisoning”). Prompt disinfection and debridement is essential for these injuries.

Electrofishing (used to stun fish during survey counts, and increasingly in collection of broodstock at hatcheries) carries a high potential for electrical shock to the operators and bystanders (National Safety Council 1985) and should be done only by trained operators, with personnel trained in cardiopulmonary resuscitation (CPR) on site. Only equipment specifically designed for electrofishing operations in water should be employed and scrupulous attention must be paid to establishing and maintaining good insulation and grounding.

All water poses drowning risks, while cold waters pose the additional hazard of hypothermia. Accidental immersions due to falls overboard must be guarded against, as must potential for ensnarement or entrapment in nets. Approved personal flotation devices should be worn by all workers at all times on or near the water, and some thermal protection should also be worn when working around cold waters (Lincoln and Klatt 1994). Mariculture personnel should be trained in marine survival and rescue techniques, as well as CPR.

Repetitive strain injuries may also occur in butchering and hand-feeding operations and can be largely avoided by attention to ergonomics (via task analysis and equipment modifications as necessary) and frequent task rotations of manual workers. Those workers developing repetitive strain injury symptoms should receive prompt evaluation and treatment and possible reassignment.

Sleep deprivation can be a risk factor for injuries in aquaculture facilities requiring intensive labour over a short duration of time (e.g., egg harvest at salmon hatcheries).

Health hazards

Diving is frequently required in construction and maintenance of fishpens. Predictably, decompression illness (“bends”) has been observed among divers not carefully observing depth/time limits (“dive tables”). There have also been reports of decompression illness occurring in divers observing these limits but making many repetitive short dives; alternative methods (not using divers) should be developed for clearing dead fish from and maintaining pens (Douglas and Milne 1991). When diving is deemed necessary, observing published dive tables, avoiding repetitive dives, always diving with a second diver (“buddy diving”) and rapid evaluation of decompression-like illnesses for possible hyperbaric oxygen therapy should be regular practices.

Severe organophosphate poisoning has occurred in workers incidental to pesticidal treatment of sea lice on salmon (Douglas 1995). Algicides deployed to control blooms may be toxic to workers, and toxic marine and freshwater algae themselves may afford worker hazards (Baxter 1991). Bath treatments for fungal infections in fish may use formaldehyde and other toxic agents (Douglas 1995). Workers must receive adequate instruction and allotment of time for safe handling of all agricultural chemicals and hygienic practices around contaminated waters.

Respiratory illnesses ranging from rhinitis to severe bronchospasm (asthma-like symptoms) have occurred due to sensitization to putative endotoxins of gram-negative bacteria contaminating farmed trout during gutting operations (Sherson, Hansen and Sigsgaard 1989), and respiratory sensitization may occur to antibiotics in medicated fish feeds. Careful attention to personal cleanliness, keeping seafood clean during butchering and handling and respiratory protection will help ensure against these problems. Workers developing sensitivity should avoid subsequent exposures to the implicated antigens. Constant immersion of hands can facilitate dermal sensitization to agricultural chemicals and foreign (fish) proteins. Hygienic practice and use of task-appropriate gloves (such as cuffed, insulated, waterproof neoprene during cold butchering operations) will reduce this risk.

Sunburn and keratotic (chronic) skin injury may result from exposure to sunlight. Wearing hats, adequate clothing and sunscreen should be de rigueur for all outdoor agricultural workers.

Large quantities of stored fish feeds are often raided by or infested with rats and other rodents, posing a risk for leptospirosis (Weil’s disease). Workers handling fish feeds must be vigilant about feed storage and rodent control and protect abraded skin and mucous membranes from contact with potentially contaminated feeds and soiled pond waters. Feeds with known contamination with rat urine should be handled as potentially infectious, and discarded promptly (Ferguson and Path 1993; Benenson 1995; Robertson et al. 1981).

Eczema and dermatitis can easily evolve from inflammation of skin macerated by constant water contact. Also, this inflammation and wet conditions can foster reproduction of human papillaviridae, leading to rapid spread of skin warts (Verruca vulgaris). Prevention is best accomplished by keeping hands as dry as possible and using appropriate gloves. Emollients are of some value in the management of minor skin irritation from water contact, but topical treatment with corticosteroids or antibiotic creams (after evaluation by a physician) may be necessary if initial treatment is unsuccessful.

Environmental Impacts

Demand for fresh water can be extremely high in all of these systems, with estimates centring on 40,000 litres required for each 0.5 kg of bony fish raised to maturity (Crowley 1995). Recirculation with filtration can greatly reduce demand, but requires intensive application of new technologies (e.g., zeolites to attract ammonia).

Fish farm discharges can include as much faecal waste as that from small cities, and regulations are rapidly proliferating for control of these discharges (Crowley 1995).

Consumption of plankton and krill, and side effects of mariculture such as algal blooms, can lead to major disruptions in species balance in the local ecosystems surrounding fish farms.

BEEKEEPING, INSECT RAISING AND SILK PRODUCTION

Melvin L. Myers and Donald Barnard*

*Some information on the silk industry was adapted from the article by J. Kubota in the 3rd edition of this Encyclopaedia.

More than a million species of insects exist in the world, and the global mass of insects exceeds the total mass of all other terrestrial animals. Insects such as crickets, grasshoppers, locusts, termites, beetle larvae, wasps, bees and moth caterpillars are among about 500 species that form part of the regular diet of people around the world. Usually humans hunt or gather insects for food rather than intentionally rearing and harvesting them.

In addition to food, humans use insects as sources of pollination, biological controls of pests and fibre. Different uses depend on the four stages of the insect’s life cycle, which consist of egg, larva, pupa and adult. Examples of commercial uses of insects include beekeeping (nearly 1 billion tonnes of honey produced annually and pollination of fruit and seed crops), insect rearing (more than 500 species in culture, including those used for insect biological control), shellac production (36,000 tonnes annually) and silk production (180,000 tonnes annually).

Beekeeping

Beekeepers raise the honey-bee in apiaries, a collection of hives that house bee colonies. The honey-bee is a source of flower pollination, honey and wax. Bees are important pollinators, making more than 46,430 foraging trips per bee for each kilogram of honey that they produce. During each foraging trip, the honey-bee will visit 500 flowers within a 25-minute period. The honey-bee’s source of honey is flower nectar. The bee uses the enzyme invertase to convert sucrose in the nectar into glucose and fructose and, with water evaporation, honey is produced. In addition, bumble-bees and cutter bees are grown for pollinating, respectively, tomato plants and alfalfa.

The honey-bee colony collects around a single queen bee, and they will colonize in boxes—artificial hives. Beekeepers establish an infant colony of about 10,000 bees in the bottom box of the hive, called a brood chamber. Each chamber contains ten panels with cells that are used for either storing honey or laying eggs. The queen lays about 1,500 eggs per day. The beekeeper then adds a food chamber super (a box placed on top of the brood box), which becomes the storage chamber for honey, on which the bees will survive through the winter. The colony continues to multiply, becoming mature at about 60,000 bees. The beekeeper adds a queen excluder (a flat panel that the larger queen cannot enter) on top of the food super to prevent the queen from laying eggs in additional shallow supers that will be stacked on top of the excluder. These additional supers are designed for harvesting only honey without the eggs.

The beekeeper moves the hives to where flowers are budding. A honey-bee colony can forage over an area of 48 hectares, and 1 hectare can support about two hives. The honey is harvested during the summer from the shallow supers, which can be stacked seven high as the colony grows and the bees fill the panels with honey. The supers with honey-laden panels are transported to the honey “house” for extraction. A sharp, warm knife, called an uncapping knife, is used to remove the wax caps that the bees have placed over the honeycombs within the panels. The honey is then extracted from the panels with a centrifugal force machine. The honey is collected and bottled for sale (Vivian 1986).

At the end of the season, the beekeeper winterizes the hives, wrapping them in tar paper to protect the colonies from the winter wind and to absorb the solar heat. The beekeeper also provides the bees with medicated sugar syrup for their winter consumption. In the spring, the hives are opened to begin production as mature honeybee colonies. If the colony becomes crowded, the colony will create another queen through special feeding, and the old queen will swarm with about half of the colony to find another accommodation. The beekeeper may capture the swarm and treat it as an infant colony.

Beekeepers are exposed to two related hazards from honey-bee stings. One hazard is sting envenomation. The other is venom hypersensitivity reaction and possible anaphylactic shock. Males at 40 years of age and older are at highest risk of fatal reactions. About 2% of the general population is thought to be allergic to venom, but systemic reactions in beekeepers and their immediate family members are estimated at 8.9%. The reaction incidence varies inversely to the numbers of stings received. Anaphylactic reactions to bumble-bee venom are rare except among bumble bee keepers, and their risk is greater if they have been sensitized to honey bee venom.

If a honey-bee stings the beekeeper, the stinger should be removed, and the sting site should be washed. Ice or a paste of baking soda and water should be applied to the site of envenomation. The victim should be watched for signs of systemic reaction, which can be a medical emergency. For anaphylactic reactions, epinephrine is administered subcutaneously at the first sign of symptoms. To assure safe beekeeping, the beekeeper should use smoke at the beehive to neutralize the bees’ protective behaviour and should wear a protective hood and veil, thin gloves and log sleeves or coveralls. Bees are attracted to sweat for the moisture, so beekeepers should not wear watch bands or belts where sweat collects. In extracting the honey, the beekeeper should keep his or her thumb and fingers clear of the cutting motion of the uncapping knife.

Mass Insect Raising

More than 500 species of arthropods are reared in the laboratory, including ants, beetles, mites, flies, moths, spiders and ticks. An important use of these arthropods is as biological controls for other animal species. For example, 2,000 years ago, markets in China sold nests of weaver ants to place in citrus orchards to prey on crop pests. Today, more than 5,000 species of insects have been identified worldwide as possible biological controls for crop pests, and 300 are successfully used regularly in 60 countries. Disease vectors have also become targets for biological control. As an example, the carnivorous mosquito from Southeast Asia, Toxorhynchites spp., also called the “tox” mosquito, has a larva that feeds on the larvae of the tiger mosquito, Aedesspp., which transmits diseases such as dengue fever to humans (O’Toole 1995).

Mass rearing facilities have been developed to raise sterile insects as a non-chemical pest-suppression tool. One such facility in Egypt rears a billion fruit flies (about 7 tonnes) each week. This rearing industry has two major cycles. One is the feed conversion or larval incubation cycle, and the other is the propagation or egg-production cycle. The sterile insect technique was first used to eliminate the screw worm, which preyed on cattle. Sterilization is accomplished by irradiating the pupae just prior to adult emergence from the cocoon with either x rays or gamma rays. This technique takes mass quantities of reared, sterile insects and releases them into infested areas where the sterile males mate with the wild, fertile females. Breaking the insect’s life cycle has dramatically reduced the fertility rate of these pests. This technique is used on screw worms, gypsy moths, boll weevils and fruit flies (Kok, Lomaliza and Shivhara 1988).

A typical sterile insect facility has an airlock system to restrict unwanted insect entry and fertile insect escape. Rearing tasks include mopping and sweeping, egg stacking, tray washing, diet preparation, inoculation (placing eggs into agar), pupae dyeing, emergence tending, packing, quarantining, irradiating, screening and weighing. In the pupae room, vermiculite is mixed with water and placed in trays. The trays are stacked, and the vermiculite dust is swept with a broom. The pupae are separated from the vermiculite with a sieve. The insect pupae chosen for the sterile insect technique are transported in trays stacked on racks to the irradiation chamber in a different area or facility, where they are irradiated and rendered sterile (Froehlich 1995; Kiefer 1996).

Insect workers, including silkworm workers, may have an allergic reaction to arthropod allergens (scales, hairs, other body parts). Initial symptoms are itchy eyes and irritation of the nose followed by intermittent episodes of wheezing, coughing and breathlessness. Subsequent asthma attacks are triggered by re-exposure to the allergen.

Entomologists and workers in sterile fly facilities are exposed to a variety of potentially hazardous, flammable agents. These agents include: in entomology laboratories, isopropyl alcohol, ethyl alcohol and xylene; in the diet preparation room, isopropyl alcohol is used in water solution to sterilize walls and ceilings with a sprayer. Vermiculite dust poses respiratory concerns. Some vermiculites are contaminated with asbestos. Air-handling units in these facilities emit noise that may be damaging to employee hearing. Proper exhaust ventilation and personal respiratory protection can be used in facilities to control exposure to airborne allergens and dusts. Non-dusty working materials should be used. Air conditioning and frequent changes of filters may help reduce airborne levels of spines and hairs. X rays or gamma rays (ionizing radiation) can damage genetic material. Protection is needed against x rays or gamma rays and their sources in the irradiation facilities (Froehlich 1995; Kiefer 1996).

Silkworm Raising

Vermiculture, the raising of worms, has a long history in some cultures. Worms, especially the meal worm (which is a larva rather than a true worm) from the darkling beetle, are raised by the billions as animal fodder for laboratory animals and pets. Worms are also used in composting operations (vermi-composting).

Sericulture is the term used for silkworm cocoon production, which includes silkworm feeding and cocoon formation. Cultivation of the silkworm and the silk moth caterpillar dates back to 3000 BC in China. Silkworm farmers have domesticated the silkworm moth; there are no remaining wild populations. Silkworms eat only white mulberry leaves. Fibre production thus has historically depended upon the leafing season of the mulberry tree. Artificial foods have been developed for the silkworm so that production can extend the year around. Silkworms are raised on trays sometimes mounted on racks. The worms take about 42 days of feeding at a constant temperature of 25 °C. Artificial heating may be required. Silk is a secretion from the silkworm’s mouth that solidifies upon contact with air. The silkworm secretes about 2 km of silk fibre to form a cocoon during the pupal stage (Johnson 1982). After the cocoon is formed, the silkworm farmer kills the pupa in a hot oven, and ships the cocoon to a factory. At the factory, silk is harvested from the cocoon and spun into thread and yarn.

Nine per cent of silkworm workers manifest asthma in response to silkworm moth scales, although most asthma in silkworm workers is attributed to inhalation of silkworm faeces. In addition, contact of the skin with silkworm caterpillar hairs may produce a primary irritant contact-dermatitis. Contact with raw silk may also produce allergic skin reactions. For silk moth production, hyposensitization therapy (for moth scales and faeces) provides improvement for 79.4% of recipients. Corticosteroids may reverse the effects of inhaled antigens. Skin lesions may respond to topical corticosteroid lotions and creams. Oral antihistamines relieve itching and burning. Carbon monoxide poisoning has been identified among some silkworm farmers in their homes, where they are maintaining warmth with charcoal fires as they raise the silkworms. Charcoal fires and kerosene heaters should be replaced with electric heaters to avoid carbon monoxide exposures.

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OTHER RELEVANT READINGS

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