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70. Livestock Rearing

Chapter Editor: Melvin L. Myers


Table of Contents

Tables and Figures

Livestock Rearing: Its Extent and Health Effects
Melvin L. Myers

Health Problems and Disease Patterns
Kendall Thu, Craig Zwerling and Kelley Donham

     Case Study: Arthopod-related Occupational Health Problems
     Donald Barnard

Forage Crops
Lorann Stallones

Livestock Confinement
Kelley Donham

Animal Husbandry
Dean T. Stueland and Paul D. Gunderson

     Case Study: Animal Behaviour
     David L. Hard

Manure and Waste Handling
William Popendorf

     A Checklist for Livestock Rearing Safety Practice
     Melvin L. Myers

Dairy
John May

Cattle, Sheep and Goats
Melvin L. Myers

Pigs
Melvin L. Myers

Poultry and Egg Production
Steven W. Lenhart

     Case Study: Poultry Catching, Live Hauling and Processing
     Tony Ashdown

Horses and Other Equines
Lynn Barroby

     Case Study: Elephants
     Melvin L. Myers

Draught Animals in Asia
D.D. Joshi

Bull Raising
David L. Hard

Pet, Furbearer and Laboratory Animal Production
Christian E. Newcomer

Fish Farming and Aquaculture
George A. Conway and Ray RaLonde

Beekeeping, Insect Raising and Silk Production
Melvin L. Myers and Donald Barnard

Tables

Click a link below to view table in article context.

1. Livestock uses
2. International livestock production (1,000 tonnes)
3. Annual US livestock faeces & urine production
4. Types of human health problems associated with livestock
5. Primary zoonoses by world region
6. Different occupations & health & safety
7. Potential arthropod hazards in the workplace
8. Normal & allergic reactions to insect sting
9. Compounds identified in swine confinement
10. Ambient levels of various gases in swine confinement
11. Respiratory diseases associated with swine production
12. Zoonotic diseases of livestock handlers
13. Physical properties of manure
14. Some important toxicologic benchmarks for hydrogen sulphide
15. Some safety procedures related to manure spreaders
16. Types of ruminants domesticated as livestock
17. Livestock rearing processes & potential hazards
18. Respiratory illnesses from exposures on livestock farms
19. Zoonoses associated with horses
20. Normal draught power of various animals

Figures

Point to a thumbnail to see figure caption, click to see figure in article context.

LIV010F2LIV010T3LIV140F1LIV110F1LIV140F1LIV070F2LIV090F1LIV090F2LIV090F3LIV090F4LIV090F6


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Overview

Humans depend upon animals for food and related by-products, work and a variety of other uses (see table 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 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 2 shows a number of these commodities and the worldwide production or consumption of these products.

Table 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 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 1. World production of meat and fish

LIV010F2

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 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 2. Human population engaged in agriculture by world region, 1994.

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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 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 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).

 

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Monday, 28 March 2011 18:46

Health Problems and Disease Patterns

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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 1). 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 1. 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 2.

Table 2. 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.

 

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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 1), 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 2 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 person’s tolerance to arthropod venom and is accomplished by injecting increasing doses of venom over time. It is effective in 90 to 100% of venom hypersensitive individuals but involves an indefinite course of expensive injections. Table 3 lists normal and allergic reactions to insect stings.

Table 1. 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 2. 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 3. 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.

 

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Monday, 28 March 2011 19:01

Forage Crops

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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.

 

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Monday, 28 March 2011 19:04

Livestock Confinement

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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 1) (Donham, Yeggy and Dauge 1988). See also the article “Manure and waste handling" in this chapter.

Table 1. 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 2. 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 2. 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 2. 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 3 summarizes the medical conditions seen in swine confinement workers.

Table 3. 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.

 

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Monday, 28 March 2011 19:08

Animal Husbandry

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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 1. Panoramic vision of cattle

LIV140F1

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 1). 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 1. 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 2).

Figure 2. Blacksmith shoeing a horse in Switzerland

LIV110F1

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.

 

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Monday, 28 March 2011 19:14

Case Study: Animal Behaviours

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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 1). 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.

Figure 1. Panoramic vision of cattle

LIV140F1

 

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Monday, 28 March 2011 19:15

Manure and Waste Handling

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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 1 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 1. 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 1 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 1, 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 2 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 2. 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 3.

 


Table 3. 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.


 

 

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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.

 

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Monday, 28 March 2011 19:23

Dairy

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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.

 

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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides