LIVESTOCK REARING: ITS EXTENT AND HEALTH EFFECTS
Humans depend upon animals for food and related by-products, work and a variety of other uses (see table 70.1). To meet these demands, they have domesticated or held in captivity species of mammals, birds, reptiles, fish and arthropods. These animals have become known as livestock, and rearing them has implications for occupational safety and health. This general profile of the industry includes its evolution and structure, the economic importance of different commodities of livestock, and regional characteristics of the industry and workforce. The articles in this chapter are organized by occupational processes, livestock sectors and consequences of livestock rearing.
Table 70.1 Livestock uses
By-products and other uses
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
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)
Hides and skins, hair, lard, manure, offal
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
Pets, furs and skins, guard dogs, seeing-eye dogs, hunting dogs, experimentation, sheep herding (by the dog), rodent control (by the cat)
Recreation (bull-fighting, rodeo riding), semen
Insects and other invertebrates (e.g., vermiculture, apiculture)
Honey, 500 species (grubs, grasshoppers, ants, crickets, termites, locusts, beetle larvae, wasps and bees, moth caterpillars) are a regular diet among many non-western societies
Beeswax, silk, predatory insects (>5,000 species are possible and 400 are known as controls for crop pests; the carnivorous �tox� mosquito (Toxorhynchites spp.) larvae feeds on the dengue fever vector, vermicompositing, animal fodder, pollination, medicine (honeybee venom to treat arthritis), scale insect products (shellac, red food dye, cochineal)
Sources: DeFoliart 1992; Gillespie 1997; FAO 1995; O�Toole 1995; Tannahil 1973; USDA 1996a, 1996b.
Evolution and structure of the industry
Livestock evolved over the past 12,000 years through selection by human communities and adaptation to new environments. Historians believe that goat and sheep were the first species of animals domesticated for human use. Then, about 9,000 years ago, humans domesticated the pig. The cow was the last major food animal that humans domesticated, about 8,000 years ago in Turkey or Macedonia. It was probably only after cattle were domesticated that milk was discovered as a useful foodstuff. Goat, sheep, reindeer and camel milk were also used. People of the Indus valley domesticated the Indian jungle fowl primarily for its egg production, which became the world�s chicken, with its source of eggs and meat. People of Mexico had domesticated the turkey (Tannahill 1973).
Humans used several other mammalian and avian species for food, as well as amphibian and fish species and various arthropods. Insects have always provided an important source of protein, and today they are part of the human diet principally in the world�s non-western cultures (DeFoliart 1992). Honey from the honey bee was an early food; smoking bees from their nest to collect honey was known in Egypt as early as 5,000 years ago. Fishing is also an ancient occupation used to produce food, but because fishers are depleting wild fisheries, aquaculture has been the fastest growing contributor to fish production since the early 1980s, contributing about 14% to the total current production of fish (Platt 1995).
Humans also domesticated many mammals for use for draught, including the horse, donkey, elephant, dog, buffalo, camel and reindeer. The first animal used for draught, perhaps with the exception of the dog, was likely the goat, which could defoliate scrub for land cultivation through its browsing. Historians believe that Asians domesticated the Asian wolf, which was to become the dog, 13,000 years ago. The dog proved to be useful to the hunter for its speed, hearing and sense of smell, and the sheepdog aided in the early domestication of sheep (Tannahill 1973). The people of the steppe lands of Eurasia domesticated the horse about 4,000 years ago. Its use for work (traction) was stimulated by the invention of the horseshoe, collar harness and feeding of oats. Although draught is still important in much of the world, farmers displace draught animals with machines as farming and transportation becomes more mechanized. Some mammals, such as the cat, are used to control rodents (Caras 1996).
The structure of the current livestock industry can be defined by commodities, the animal products that enter the market. Table 70.2 shows a number of these commodities and the worldwide production or consumption of these products.
Table 70.2 International livestock production (1,000 tonnes)
Beef and veal carcasses
Lamb, mutton, goat carcasses
Bovine hides and skins
Tallow and grease
Egg consumption (million pieces)
Sources: FAO 1995; USDA 1996a, 1996b.
The world�s growing population and increased per capita consumption both increased the global demand for meat and fish, the results of which are shown in figure 70.1 . Global meat production nearly trebled between 1960 and 1994. Over this period, per capita consumption increased from 21 to 33 kilograms per annum. Because of the limitations of available rangeland, beef production levelled off in 1990. As a result, animals that are more efficient in converting feed grain into meat, such as pigs and chickens, have gained a competitive advantage. Both pork and poultry have been increasing in dramatic contrast to beef production. Pork overtook beef in worldwide production in the late 1970s. Poultry may soon exceed beef production. Mutton production remains low and stagnant (USDA 1996a). Milk cows worldwide have been slowly decreasing while milk production has been increasing because of increasing production per cow (USDA 1996b).
Figure 70.1 World production of meat and fish
Sources: Brown 1995; Platt 1995.
Aquaculture production increased at an annual rate of 9.1% from 1984 to 1992. Aquaculture animal production increased from 14 million tonnes worldwide in 1991 to 16 million tonnes in 1992, with Asia providing 84% of world production (Platt 1995). Insects are rich in vitamins, minerals and energy, and provide between 5% and 10% of the animal protein for many people. They also become a vital source of protein during times of famine (DeFoliart 1992).
Regional Characteristics of the Industry and Workforce
Separating the workforce engaged in livestock rearing from other agricultural activities is difficult. Pastoral activities, such as those in much of Africa, and heavy commodity-based operations, such as those in the United States, have differentiated more between livestock and crop raising. However, many agro-pastoral and agronomic enterprises integrate the two. In much of the world, draught animals are still used extensively in crop production. Moreover, livestock and poultry depend upon feed and forage generated from crop operations, and these operations are commonly integrated. The principal aquaculture species in the world is the plant-eating carp. Insect production is also tied directly to crop production. The silkworm feeds exclusively on mulberry leaves; honeybees depend upon flower nectar; plants depend upon them for pollination work; and humans harvest edible grubs from various crops. The 1994 world population totalled 5,623,500,000, and 2,735,021,000 people (49% of the population) were engaged in agriculture (see figure 70.2). The largest contribution to this workforce is in Asia, where 85% of the agricultural population rear draught animals. Regional characteristics related to livestock rearing follow.
Figure 70.2 Human population engaged in agriculture by world region, 1994
Source: Scherf 1995.
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.
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.
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.
Although agriculture is a major economic activity in Canada and the United States, the proportion of the population engaged in agriculture is less than 2.5%. Since the 1950s, agriculture has become more intensive, leading to fewer but larger farms. Livestock and livestock products make up a major proportion of the population�s diet, contributing 40% to the total food energy. The livestock industry in this region has been very dynamic. Introduced animals have been bred with indigenous animals to form new breeds. Consumer demand for leaner meats and eggs with less cholesterol is having an impact on breeding policy. Horses were used extensively at the turn of the nineteenth century, but they have declined in numbers because of mechanization. They are currently used in the race horse industry or for recreation. The United States has imported about 700 insect species to control more than 50 pests. Aquaculture in this region is growing, and accounted for 3.7% of the world�s aquaculture production in 1992 (FAO 1995; Scherf 1995).
Environmental and Public Health Issues
Occupational hazards of livestock rearing may lead to injuries, asthma or zoonotic infections. In addition, livestock rearing poses several environmental and public health issues. One issue is the effect of animal waste upon the environment. Other issues include the loss of biological diversity, risks associated with animal and product importation and food safety.
Water and air pollution
Animal wastes pose potential environmental consequences of water and air pollution. Based upon US annual discharge factors shown in table 70.3 , major livestock breeds discharged a total of 14.3 billion tonnes of faeces and urine worldwide in 1994. Of this total, cattle (milk and beef) discharged 87%; pigs, 9%; and chickens and turkeys, 3% (Meadows 1995). Because of their high annual discharge factor of 9.76 tonnes of faeces and urine per animal, cattle contributed the most waste among these livestock types for all six United Nations Food and Agricultural Organization (FAO) regions of the world, ranging from 82% in both Europe and Asia to 96% in sub-Saharan Africa.
Table 70.3 Annual US livestock faeces and urine production
Tonnes per animal
Cattle (milk and beef)
Chicken and turkey
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.
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).
Many human food-borne illnesses result from pathogenic bacteria of animal origin. Examples include listeria and salmonellae found in dairy products and salmonellae and campylobacter found in meat and poultry. The Centers for Disease Control and Prevention estimates that 53% of all food-borne illness outbreaks in the United States were caused by bacterial contamination of animal products. They estimate that 33 million food-borne illnesses occur each year, from which 9,000 deaths result.
The subtherapeutic feeding of antibiotics and antibiotic treatment of diseased animals are current animal health practices. The potential diminished effectiveness of antibiotics for disease therapy is a rising concern because of the frequent development of antibiotic resistance of zoonotic pathogens. Many antibiotics added to animal feed are also used in human medicine, and antibiotic-resistant bacteria could develop and cause infections in animals and humans.
Drug residues in food that result from medication of livestock also present risks. Residues of antibiotics used in livestock or added to feed have been found in food-producing animals including dairy cows. Among these drugs are chloramphenicol and sulphamethazine. Alternatives to the prophylactic feeding use of antibiotics to maintain animal health include the modification of production systems. These modifications include reduced animal confinement, improved ventilation and improved waste treatment systems.
Diet has been associated with chronic diseases. Evidence of an association between fat consumption and heart disease has stimulated efforts to produce animal products with less fat content. These efforts include animal breeding, feeding intact rather than castrated males and genetic engineering. Hormones are also seen as a method for decreasing fat content in meat. Porcine growth hormones increase growth rate, feed efficiency and the ratio of muscle to fat. The growing popularity of low-fat, low-cholesterol species such as ostriches is another solution (NRC 1989).
HEALTH PROBLEMS AND DISEASE PATTERNS
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.
Types of human health problems and disease patterns associated with livestock production can be grouped according to the type of contact between animals and people (see table 70.4). Contact can occur via direct physical interaction, or contact with an organic or inorganic agent. Health problems associated with all types of livestock production can be grouped into each of these areas.
Table 70.4 Types of human health problems associated with livestock production
Health problems from direct physical contact
Health problems from organic agents
Health problems from physical agents
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.
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.
Zoonotic diseases can be classified according to their modes of transmission, which are in turn linked to forms of agriculture, human social organization and the ecosystem. The four general routes of transmission are:
1. direct single vertebrate host
2. cyclical multiple vertebrate host
3. combination vertebrate-invertebrate host
4. inanimate intermediary host.
Zoonotic diseases can be generally characterized as follows: they are non-fatal, infrequently diagnosed and sporadic rather than epidemic; they mimic other diseases; and humans are typically the dead-end hosts. Primary zoonotic diseases by region are listed in table 70.5 .
Table 70.5 Primary zoonoses by world region
Eastern Mediterranean, West and Southeast Asia, Latin America
Goats, sheep, cattle, swine
Europe, Mediterranean area, United States
Birds, sheep, rodents
Africa, Australia, Central Europe, Far East, Latin America, Russia, United States
Dogs, ruminants, swine, wild carnivores
Eastern Mediterranean, southern South America, South and East Africa, New Zealand, southern Australia, Siberia
Rodents, cattle, swine, wild carnivores, horses
Worldwide, more prevalent in Caribbean
Cattle, goats, sheep
Dogs, cats, wild carnivores, bats
Worldwide, most prevalent in regions with industrial agriculture and higher use of antibiotics
Swine, wild carnivores, Arctic animals
Argentina, Brazil, Central Europe, Chile North America, Spain
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.
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 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.
The number of livestock worldwide has grown apace with the increase in human population. There are approximately 4 billion cattle, pigs, sheep, goats, horses, buffalo and camels in the world (Durning and Brough 1992). However, there is a notable lack of data on livestock-related human health problems in developing areas of the world such as China and India, where much of the livestock currently reside and where future growth is likely to occur. However, given the emergence of industrialized agriculture worldwide, it can be anticipated that many of the health problems documented in North American and European livestock production will likely accompany the emergence of industrialized livestock production elsewhere. It is also anticipated that health services in these areas will be inadequate to deal with the health and safety consequences of industrialized livestock production generally described here.
The worldwide emergence of industrialized livestock production with its attendant human health consequences will accompany fundamental changes in the social, economic and political order comparable to those that followed from the domestication of animals over 10,000 years ago. Preventing human health problems will require broad understanding and appropriate engagement of these new forms of human adaptation and the place of livestock production within them.
ARTHROPOD-RELATED OCCUPATIONAL HEALTH PROBLEMS
Arthropods comprise more than 1 million species of insects and thousands of species of ticks, mites, spiders, scorpions and centipedes. Bees, ants, wasps and scorpions sting and inject venom; mosquitoes and ticks suck blood and transmit diseases; and the scales and hairs from insect bodies can irritate the eyes and skin, as well as tissues in the nose, mouth and respiratory system. Most stings in humans are from social bees (bumble bees, honey bees). Other stings are from paper wasps, yellow jackets, hornets and ants.
Arthropods can be a health hazard in the workplace (see table 70.6), but in most cases, potential arthropod hazards are not unique to specific occupations. Rather, exposure to arthropods in the workplace depends on geographic location, local conditions and the time of year. Table 70.7 lists some of these hazards and their corresponding arthropod agents. For all arthropod hazards, the first line of defence is avoidance or exclusion of the offending agent. Venom immunotherapy may increase a persons's tolerance to arthropod venom and is accomplished by injecting increasing doses of venom over time. It is effective in 90 to 100% of cenom hypersensitive individuals but involves an indefinite course of expensive injections. Table 70.8 lists normal and allergic reactions to insect stings.
Table 70.6 Different occupations and their potential for contact with arthropods that may adversely affect health and safety.
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
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
Table 70.7 Potential arthropod hazards in the workplace and their causative agent(s)
Ants, biting flies, centipedes, mites, spiders
Sting envenomation, venom hypersensitivity2
Ants, bees, wasps, scorpions
Beetles, caddisflies, caterpillars, cockroaches, crickets, dust mites, fly maggots, grain mites, grain weevils, grasshoppers, honeybees, mayflies, moths, silk worms
Blister beetles, caterpillars, cockroaches, dried fruit mites, dust mites, grain mites, straw itch mites, moths, silk worms, spiders
1 Envenomation with poison from glands associated with mouthparts.
2 Envenomation with poison from glands not associated with mouthparts.
3 Includes primary irritant and allergic dermatitis.
Table 70.8 Normal and allergic reactions to insect sting
Type of response
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.
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.
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 foragehay and silageis 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 placeda task called buckingonto 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.
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
Respiratory hazards are also a concern.
Toxic and Asphyxiating Gases
Several toxic and asphyxiating gases resulting from microbial degradation of animal wastes (urine and faeces) may be associated with livestock confinement. Wastes are most commonly stored in liquid form under the building, over a slatted floor or in a tank or lagoon outside the building. This manure storage system is usually anaerobic, leading to the formation of a number of toxic gases (see table 70.9) (Donham, Yeggy and Dauge 1988). See also the article �Manure and waste handling� in this chapter.
Table 70.9 Compounds identified in swine confinement building atmospheres
Heterocylic nitrogen compound
There are four common toxic or asphyxiating gases present in almost every operation where anaerobic digestion of wastes occurs: carbon dioxide (CO2), ammonia (NH3), hydrogen sulphide (H2S) and methane (CH4). A small amount of carbon monoxide (CO) may also be produced by the decomposing animal wastes, but its main source is heaters used to burn fossil fuels. Typical ambient levels of these gases (as well as particulates) in swine confinement buildings are shown in table 70.10 . Also listed are maximum recommended exposures in swine buildings based on recent research (Donham and Reynolds 1995; Reynolds et al. 1996) and threshold limit values (TLVs) set by the American Conference of Governmental Industrial Hygienists (ACGIH 1994). These TLVs have been adopted as legal limits in many countries.
Table 70.10 Ambient levels of various gases in swine confinement buildings
Typical ambient concentrations (ppm)
Recommended maximum exposure concentrations (ppm)
Threshold limit values (ppm)
0 to 200
1,000 to 10,000
5 to 200
0 to 1,500
2 to 15 mg/m3
0.10 to 1.0 mg/m3
50 to 500 ng/m3
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 synergisticthe TLV for the mixture may be exceeded even when individual TLVs are not exceeded. Concentrations are often higher in the winter than in the summer, because ventilation is reduced to conserve heat.
These gases have been implicated in several acute conditions in workers. H2S has been implicated in many sudden animal deaths and several human deaths (Donham and Knapp 1982). Most acute cases have occurred shortly after the manure pit has been agitated or emptied, which may result in a sudden release of a large volume of the acutely toxic H2S. In other fatal cases, manure pits had recently been emptied, and workers who entered the pit for inspection, repairs or to retrieve a dropped object collapsed without any forewarning. The available post-mortem results of these cases of acute poisoning revealed massive pulmonary oedema as the only notable finding. This lesion, combined with the history, is compatible with hydrogen sulphide intoxication. Rescue attempts by bystanders have often resulted in multiple fatalities. Confinement workers should therefore be informed of the risks involved and advised never to enter a manure storage facility without testing for the presence of toxic gases, being equipped with a respirator with its own oxygen supply, ensuring adequate ventilation and having at least two other workers stand by, attached by a rope to the worker who enters, so they can effect a rescue without endangering themselves. There should be a written confined-space programme.
CO may also be present at acute toxic levels. Abortion problems in swine at an atmospheric concentration of 200 to 400 ppm and subacute symptoms in humans, such as chronic headache and nausea, have been documented in swine confinement systems. The possible effects on the human foetus should also be of concern. The primary source of CO is from improperly functioning hydrocarbon-burning heating units. Heavy accumulation of dust in swine confinement buildings makes it difficult to keep heaters in correct working order. Propane-fuelled radiant heaters are also a common source of lower levels of CO (e.g., 100 to 300 ppm). High-pressure washers powered by an internal combustion engine that may be run inside the building are another source; CO alarms should be installed.
Another acutely dangerous situation occurs when the ventilation system fails. Gas levels may then rapidly build up to critical levels. In this case the major problem is replacement of oxygen by other gases, primarily CO2 produced from the pit as well as from the respiratory activity of the animals in the building. Lethal conditions could be reached in as few as 7 hours. Regarding the health of the pigs, ventilation failure in warm weather may allow temperature and humidity to increase to lethal levels in 3 hours. Ventilation systems should be monitored.
A fourth potentially acute hazard arises from build-up of CH4, which is lighter than air and, when emitted from the manure pit, tends to accumulate in the upper portions of the building. There have been several instances of explosions occurring when the CH4 accumulation was ignited by a pilot light or a worker�s welding torch.
Bioactive Aerosols of Particulates
The sources of dust in confinement buildings are a combination of feed, dander and hair from the swine and dried faecal material (Donham and Scallon 1985). The particulates are about 24% protein and therefore have the potential not only for initiating an inflammatory response to foreign protein but also for initiating an adverse allergic reaction. The majority of particles are smaller than 5 microns, allowing them to be respired into the deep portions of the lungs, where they may produce a greater danger to health. The particulates are laden with microbes (104 to 107/m3 air). These microbes contribute several toxic/inflammatory substances including, among others, endotoxin (the most documented hazard), glucans, histamine and proteases. The recommended maximum concentrations for dusts are listed in table 70.10 . Gases present within the building and bacteria in the atmosphere are adsorbed on the surface of the dust particles. Thus, the inhaled particles have the increased potentially hazardous effect of carrying irritating or toxic gases as well as potentially infectious bacteria into the lungs.
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 levels of 103 dBA have been measured within animal confinement buildings; this is above the TLV, and offers a potential for noise-induced hearing loss (Donham, Yeggy and Dauge 1988).
Respiratory Symptoms of Livestock Confinement Workers
The general respiratory hazards within livestock confinement buildings are similar regardless of the species of livestock. However, swine confinements are associated with adverse health effects in a larger percentage of workers (25 to 70% of active workers), with more severe symptoms than those in poultry or cattle confinements (Rylander et al. 1989). The waste in poultry facilities is usually handled in solid form, and in this instance ammonia seems to be the primary gaseous problem; hydrogen sulphide is not present.
Subacute or chronic respiratory symptoms reported by confinement workers have been observed to be most frequently associated with swine confinement. Surveys of swine confinement workers have revealed that about 75% suffer from adverse acute upper respiratory symptoms. These symptoms can be broken down into three groups:
1. acute or chronic inflammation of the respiratory airways (manifested as bronchitis)
2. acquired occupational (non-allergic) constriction of the airways (asthma)
3. delayed self-limited febrile illness with generalized symptoms (organic dust toxic syndrome (ODTS)).
Symptoms suggestive of chronic inflammation of the upper respiratory system are common; they are seen in about 70% of swine confinement workers. Most commonly, they include tightness of the chest, coughing, wheezing and excess sputum production.
In approximately 5% of workers, symptoms develop after working in the buildings for only a few weeks. The symptoms include chest tightness, wheezing and difficult breathing. Usually these workers are affected so severely that they are forced to seek employment elsewhere. Not enough is known to indicate whether this reaction is an allergic hypersensitivity or a non-allergic hypersensitivity to dust and gas. More typically, symptoms of bronchitis and asthma develop after 5 years of exposure.
Approximately 30% of workers occasionally experience episodes of delayed symptoms. Approximately 4 to 6 hours after working in the building they develop a flu-like illness manifested by fever, headache, malaise, general muscle aches and chest pain. They usually recover from these symptoms in 24 to 72 hours. This syndrome has been recognized as ODTS.
The potential for chronic lung damage certainly seems to be real for these workers. However, this has not been documented so far. It is recommended that certain procedures be followed to prevent chronic exposure as well as acute exposure to the hazardous materials in swine confinement buildings. Table 70.11 summarizes the medical conditions seen in swine confinement workers.
Table 70.11 Respiratory diseases associated with swine production
Upper airway disease
Lower airway disease
Non-allergic asthma, hyperresponsive airways disease, or reactive airways disease syndrome (RADS)
Allergic asthma (IgE mediated)
Acute or subacute bronchitis
Chronic obstructive pulmonary disease (COPD)
Chronic interstitial infiltrate
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.
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.
The livestock sector globally is highly dynamic. In developing countries, it is evolving in response to rapidly increasing demand for livestock products. In developed countries, demand for livestock products is stagnating, while many production systems are increasing their efficiency and environmental sustainability. Historical changes in the demand for livestock products have been largely driven by human population growth, income growth and urbanization and the production response in different livestock systems has been associated with science and technology as well as increases in animal numbers. In the future, production will increasingly be affected by competition for natural resources, particularly land and water, competition between food and feed and by the need to operate in a carbon-constrained economy. Developments in breeding, nutrition and animal health will continue to contribute to increasing potential production and further efficiency and genetic gains. Livestock production is likely to be increasingly affected by carbon constraints and environmental and animal welfare legislation. Demand for livestock products in the future could be heavily moderated by socio-economic factors such as human health concerns and changing socio-cultural values. There is considerable uncertainty as to how these factors will play out in different regions of the world in the coming decades.
Keywords: supply, demand, scenario, development, poverty, sustainability
Livestock systems occupy about 30 per cent of the planet's ice-free terrestrial surface area (Steinfeld et al. 2006) and are a significant global asset with a value of at least $1.4 trillion. The livestock sector is increasingly organized in long market chains that employ at least 1.3 billion people globally and directly support the livelihoods of 600 million poor smallholder farmers in the developing world (Thornton et al. 2006). Keeping livestock is an important risk reduction strategy for vulnerable communities, and livestock are important providers of nutrients and traction for growing crops in smallholder systems. Livestock products contribute 17 per cent to kilocalorie consumption and 33 per cent to protein consumption globally, but there are large differences between rich and poor countries (Rosegrant et al. 2009).
Livestock systems have both positive and negative effects on the natural resource base, public health, social equity and economic growth (World Bank 2009). Currently, livestock is one of the fastest growing agricultural subsectors in developing countries. Its share of agricultural GDP is already 33 per cent and is quickly increasing. This growth is driven by the rapidly increasing demand for livestock products, this demand being driven by population growth, urbanization and increasing incomes in developing countries (Delgado 2005).
The global livestock sector is characterized by a dichotomy between developing and developed countries. Total meat production in the developing world tripled between 1980 and 2002, from 45 to 134 million tons (World Bank 2009). Much of this growth was concentrated in countries that experienced rapid economic growth, particularly in East Asia, and revolved around poultry and pigs. In developed countries, on the other hand, production and consumption of livestock products are now growing only slowly or stagnating, although at high levels. Even so, livestock production and merchandizing in industrialized countries account for 53 per cent of agricultural GDP (World Bank 2009). This combination of growing demand in the developing world and stagnant demand in industrialized countries represents a major opportunity for livestock keepers in developing countries, where most demand is met by local production, and this is likely to continue well into the foreseeable future. At the same time, the expansion of agricultural production needs to take place in a way that allows the less well-off to benefit from increased demand and that moderates its impact on the environment.
This paper attempts a rapid summary of the present-day state of livestock production systems globally in relation to recent trends, coupled with a brief assessment of whether these trends are likely to continue into the future. In §2, the key drivers underpinning past increases in livestock production are outlined, and the status of both intensive and extensive production systems in the developed and developing world is described. Section 3 summarizes the advances in science and technology that have contributed to historical increases in livestock production, and indicates where potential remains, in relation to livestock genetics and breeding, livestock nutrition and livestock disease management. Section 4 contains sketches of a number of factors that may modify both the production and the consumption of livestock products in the future: competition for land and water, climate change, the role of socio-cultural drivers and ethical concerns. (Competition for resources and climate change are treated very briefly: other reviews address these issues comprehensively.) The section concludes with a brief discussion of three ‘wildcards’, chosen somewhat arbitrarily, that could cause considerable upheaval to future livestock production and consumption trends in the future: artificial meat, nanotechnology and deepening social concern over new technology. The paper concludes (§5) with a summary outlook on livestock production systems evolution over the coming decades and some of the key uncertainties.
2. Trends in livestock production and livestock systems evolution
(a) The increasing demand for livestock products
Human population in 2050 is estimated to be 9.15 billion, with a range of 7.96–10.46 billion (UNPD 2008). Most of the increase is projected to take place in developing countries. East Asia will have shifted to negative population growth by the late 2040s (FAO 2010). In contrast, population in sub-Saharan Africa (SSA) will still be growing at 1.2 per cent per year. Rapid population growth could continue to be an important impediment to achieving improvements in food security in some countries, even when world population as a whole ceases growing sometime during the present century. Another important factor determining demand for food is urbanization. As of the end of 2008, more people now live in urban settings than in rural areas (UNFPA 2008), with urbanization rates varying from less than 30 per cent in South Asia to near 80 per cent in developed countries and Latin America. The next few decades will see unprecedented urban growth, particularly in Africa and Asia. Urbanization has considerable impact on patterns of food consumption in general and on demand for livestock products in particular: urbanization often stimulates improvements in infrastructure, including cold chains, and this allows perishable goods to be traded more widely (Delgado 2005). A third driver leading to increased demand for livestock products is income growth. Between 1950 and 2000, there was an annual global per capita income growth rate of 2.1 per cent (Maddison 2003). As income grows, so does expenditure on livestock products (Steinfeld et al. 2006). Economic growth is expected to continue into the future, typically at rates ranging from between 1.0 and 3.1 per cent (van Vuuren et al. 2009). Growth in industrialized countries is projected to be slower than that in developing economies (Rosegrant et al. 2009).
The resultant trends in meat and milk consumption figures in developing and developed countries are shown in table 1, together with estimates for 2015–2050 (FAO 2006; Steinfeld et al. 2006). Differences in the consumption of animal products are much greater than in total food availability, particularly between regions. Food demand for livestock products will nearly double in sub-Saharan Africa and South Asia, from some 200 kcal per person per day in 2000 to around 400 kcal per person per day in 2050. On the other hand, in most OECD countries that already have high calorie intakes of animal products (1000 kcal per person per day or more), consumption levels will barely change, while levels in South America and countries of the Former Soviet Union will increase to OECD levels (Van Vuuren et al. 2009).
Past and projected trends in consumption of meat and milk in developing and developed countries. Data for 1980–2015 adapted from Steinfeld et al. (2006) and for 2030–2050 from FAO (2006). Projections are shown in italic font.
The agricultural production sector is catering increasingly to globalized diets. Retailing through supermarkets is growing at 20 per cent per annum in countries such as China, India and Vietnam, and this will continue over the next few decades as urban consumers demand more processed foods, thus increasing the role of agribusiness (Rosegrant et al. 2009).
(b) The production response
Global livestock production has increased substantially since the 1960s. Beef production has more than doubled, while over the same time chicken meat production has increased by a factor of nearly 10, made up of increases in both number of animals and productivity (figure 1). Carcass weights increased by about 30 per cent for both chicken and beef cattle from the early 1960s to the mid-2000s, and by about 20 per cent for pigs (FAO 2010). Carcass weight increases per head for camels and sheep are much less, about 5 per cent only over this time period. Increases in milk production per animal have amounted to about 30 per cent for cows' milk, about the same as for increases in egg production per chicken over the same time period (FAO 2010).
(a) Number of chickens, carcass weight and egg production per animal from 1961 to 2008, global. (b) Number of bovines (cattle and buffaloes), carcass weight and cattle milk production per animal from 1961 to 2008, global. (c) Number of pigs and carcass...
These changes have been accompanied by substantial shifts in the area of arable land, pastures and forest. Arable and pasture lands have expanded considerably since the early 1960s, although the rates of change have started to slow (Steinfeld et al. 2006). Over the last 20 years, large forest conversions have occurred in the Amazon Basin, Southeast Asia and Central and West Africa, while forest area has increased owing to agricultural land abandonment in the Eurasian boreal forest and parts of Asia, North America, and Latin America and the Caribbean (LAC) (GEO4 2007). Considerable expansion of crop land planted to soybean (as a protein source in animal feed) has occurred in Latin America over the last 30 years. Developing countries' share of global use of cereals for animal feed nearly doubled (to 36%) from the early 1908s to the late 1990s (Delgado 2005). Some cropland has been converted to other uses, including urban development around many major cities. Land-use intensity has increased in some places: cereal yields have trebled in East Asia over this time, while yields have increased not at all in sub-Saharan Africa, for example. Land-use change is complex and driven by a range of drivers that are regionally specific, although it is possible to see some strong historical associations between land abundance, application of science and technology and land-use change in some regions (Rosegrant et al. 2009). In Latin America, for instance, land abundance has slowed the introduction of new technologies that can raise productivity.
Historically, production response has been characterized by systems' as well as regional differences. Confined livestock production systems in industrialized countries are the source of much of the world's poultry and pig meat production, and such systems are being established in developing countries, particularly in Asia, to meet increasing demand. Bruinsma (2003) estimates that at least 75 per cent of total production growth to 2030 will be in confined systems, but there will be much less growth of these systems in Africa.
While crop production growth will come mostly from yield increases rather than from area expansion, the increases in livestock production will come about more as a result of expansion in livestock numbers in developing countries, particularly ruminants. In the intensive mixed systems, food-feed crops are vital ruminant livestock feed resources. The prices of food-feed crops are likely to increase at faster rates than the prices of livestock products (Rosegrant et al. 2009). Changes in stover production will vary widely from region to region out to 2030 (Herrero et al. 2009). Large increases may occur in Africa mostly as a result of productivity increases in maize, sorghum and millet. Yet stover production may stagnate in areas such as the ruminant-dense mixed systems of South Asia, and stover will need to be replaced by other feeds in the diet to avoid significant feed deficits. The production of alternative feeds for ruminants in the more intensive mixed systems, however, may be constrained by both land and water availability, particularly in the irrigated systems (Herrero et al. 2009).
Meeting the substantial increases in demand for food will have profound implications for livestock production systems over the coming decades. In developed countries, carcass weight growth will contribute an increasing share of livestock production growth as expansion of numbers is expected to slow; numbers may contract in some regions. Globally, however, between 2000 and 2050, the global cattle population may increase from 1.5 billion to 2.6 billion, and the global goat and sheep population from 1.7 billion to 2.7 billion (figure 2; Rosegrant et al. 2009). Ruminant grazing intensity in the rangelands is projected to increase, resulting in considerable intensification of livestock production in the humid and subhumid grazing systems of the world, particularly in LAC.
(a) Projected number of (i) bovines and (ii) sheep and goats to 2050 in the ‘reference world’. (b) Projected number of (i) pigs and (ii) poultry to 2050 in the ‘reference world’. CWANA, Central and West Asia and North Africa;...
The prices of meats, milk and cereals are likely to increase in the coming decades, dramatically reversing past trends. Rapid growth in meat and milk demand may increase prices for maize and other coarse grains and meals. Bioenergy demand is projected to compete with land and water resources, and this will exacerbate competition for land from increasing demands for feed resources. Growing scarcities of water and land will require substantially increased resource use efficiencies in livestock production to avoid adverse impacts on food security and human wellbeing goals. Higher prices can benefit surplus agricultural producers, but can reduce access to food by a larger number of poor consumers, including farmers who do not produce a net surplus for the market. As a result, progress in reducing malnutrition is projected to be slow (Rosegrant et al. 2009). Livestock system evolution in the coming decades is inevitably going to involve trade-offs between food security, poverty, equity, environmental sustainability and economic development.
3. Livestock science and technology as a driver of change
(a) Breeding and genetics
Historically, domestication and the use of conventional livestock breeding techniques have been largely responsible for the increases in yield of livestock products that have been observed over recent decades (Leakey et al. 2009). At the same time, considerable changes in the composition of livestock products have occurred. If past changes in demand for livestock products have been met by a combination of conventional techniques, such as breed substitution, cross-breeding and within-breed selection, future changes are likely to be met increasingly from new techniques.
Of the conventional techniques, selection among breeds or crosses is a one-off process, in which the most appropriate breed or breed cross can be chosen, but further improvement can be made only by selection within the population (Simm et al. 2004). Cross-breeding, widespread in commercial production, exploits the complementarity of different breeds or strains and makes use of heterosis or hybrid vigour (Simm 1998). Selection within breeds of farm livestock produces genetic changes typically in the range 1–3% per year, in relation to the mean of the single or multiple traits that are of interest (Smith 1984). Such rates of change have been achieved in practice over the last few decades in poultry and pig breeding schemes in several countries and in dairy cattle breeding programmes in countries such as the USA, Canada and New Zealand (Simm 1998), mostly because of the activities of breeding companies. Rates of genetic change achieved in national beef cattle and sheep populations are often substantially lower than what is theoretically possible. Ruminant breeding in most countries is often highly dispersed, and sector-wide improvement is challenging.
Rates of genetic change have increased in recent decades in most species in developed countries for several reasons, including more efficient statistical methods for estimating the genetic merit of animals, the wider use of technologies such as artificial insemination and more focused selection on objective traits such as milk yield (Simm et al. 2004). The greatest gains have been made in poultry and pigs, with smaller gains in dairy cattle, particularly in developed countries and in the more industrialized production systems of some developing countries. Some of this has been achieved through the widespread use of breed substitution, which tends to lead to the predominance of a few highly specialized breeds, within which the genetic selection goals may be narrowly focused.
While most of the gains have occurred in developed countries, there are considerable opportunities to increase productivity in developing countries. Within-breed selection has not been practised all that widely, in part because of the lack of the appropriate infrastructure needed (such as performance recording and genetic evaluation schemes). Breed substitution or crossing can result in rapid improvements in productivity, but new breeds and crosses need to be appropriate for the environment and to fit within production systems that may be characterized by limited resources and other constraints. High-performing temperate breeds of dairy cow may not be appropriate for some developing-country situations: for example, heat stress and energy deficits make the use of Friesians in smallholdings on the Kenyan coast unsustainable, partly because of low cow replacement rates (King et al. 2006a). There is much more potential in the use of crosses of European breeds with local Zebus that are well-adapted to local conditions.
In the future, many developed countries will see a continuing trend in which livestock breeding focuses on other attributes in addition to production and productivity, such as product quality, increasing animal welfare, disease resistance and reducing environmental impact. The tools of molecular genetics are likely to have considerable impact in the future. For example, DNA-based tests for genes or markers affecting traits that are difficult to measure currently, such as meat quality and disease resistance, will be particularly useful (Leakey et al. 2009). Another example is transgenic livestock for food production; these are technically feasible, although the technologies associated with livestock are at an earlier stage of development than the equivalent technologies in plants. In combination with new dissemination methods such as cloning, such techniques could dramatically change livestock production. Complete genome maps for poultry and cattle now exist, and these open up the way to possible advances in evolutionary biology, animal breeding and animal models for human diseases (Lewin 2009). Genomic selection should be able to at least double the rate of genetic gain in the dairy industry (Hayes et al. 2009), as it enables selection decisions to be based on genomic breeding values, which can ultimately be calculated from genetic marker information alone, rather than from pedigree and phenotypic information. Genomic selection is not without its challenges, but it is likely to revolutionize animal breeding.
As the tools and techniques of breeding are changing, so are the objectives of many breeding programmes. Although there is little evidence of direct genetic limits to selection for yield, if selection is too narrowly focused there may be undesirable associated responses (Simm et al. 2004); for example, in dairy cattle, where along with genetic gain in some production traits, there is now considerable evidence of undesirable genetic changes in fertility, disease incidence and overall stress sensitivity, despite improved nutrition and general management (Hare et al. 2006). Trade-offs are likely to become increasingly important, between breeding for increased efficiency of resource use, knock-on impacts on fertility and other traits and environmental impacts such as methane production. Whole-system and life-cycle analyses (‘cradle-to-grave’ analyses that assess the full range of relevant costs and benefits) will become increasingly important in disentangling these complexities.
New tools of molecular genetics may have far-reaching impacts on livestock and livestock production in the coming decades. But ultimately, whether the tools used are novel or traditional, all depend on preserving access to animal genetic resources. In developing countries, if livestock are to continue to contribute to improving livelihoods and meeting market demands, the preservation of farm animal genetic resources will be critical in helping livestock adapt to climate change and the changes that may occur in these systems, such as shifts in disease prevalence and severity. In developed countries, the narrowing animal genetic resource base in many of the intensive livestock production systems demonstrates a need to maintain as broad a range of genetic resources as possible, to provide genetic insurance against future challenges and shocks. Institutional and policy frameworks that encourage the sustainable use of traditional breeds and in situ conservation need to be implemented, and more understanding is needed of the match between livestock populations, breeds and genes with the physical, biological and economic landscape (FAO 2007).
The nutritional needs of farm animals with respect to energy, protein, minerals and vitamins have long been known, and these have been refined in recent decades. Various requirement determination systems exist in different countries for ruminants and non-ruminants, which were originally designed to assess the nutritional and productive consequences of different feeds for the animal once intake was known. However, a considerable body of work exists associated with the dynamics of digestion, and feed intake and animal performance can now be predicted in many livestock species with high accuracy.
A large agenda of work still remains concerning the robust prediction of animal growth, body composition, feed requirements, the outputs of waste products from the animal and production costs. Such work could go a long way to help improve the efficiency of livestock production and meeting the expectations of consumers and the demands of regulatory authorities. Advances in genomics, transcriptomics, proteomics and metabolomics will continue to contribute to the field of animal nutrition and predictions relating to growth and development (Dumas et al. 2008). Better understanding of the processes involved in animal nutrition could also contribute to improved management of some of the trade-offs that operate at high levels of animal performance, such as those associated with lower reproductive performance (Butler 2000).
While understanding of the science of animal nutrition continues to expand and develop, most of the world's livestock, particularly ruminants in pastoral and extensive mixed systems in many developing countries, suffer from permanent or seasonal nutritional stress (Bruinsma 2003). Poor nutrition is one of the major production constraints in smallholder systems, particularly in Africa. Much research has been carried out to improve the quality and availability of feed resources, including work on sown forages, forage conservation, the use of multi-purpose trees, fibrous crop residues and strategic supplementation. There are also prospects for using novel feeds from various sources to provide alternative sources of protein and energy, such as plantation crops and various industrial (including ethanol) by-products. The potential of such feeds is largely unknown. Given the prevalence of mixed crop–livestock systems in many parts of the world, closer integration of crops and livestock in such systems can give rise to increased productivity and increased soil fertility (McIntire et al. 1992). In such systems, smallholders use crops for multiple purposes (food and feed, for example), and crop breeding programmes are now well established that are targeting stover quality as well as grain yield in crops such as maize, sorghum, millet and groundnut.
Considerable work is under way to address some of the issues associated with various antinutritional factors. These include methods to reduce the tannin content of tree and shrub material, the addition of essential oils that may be beneficial in ruminant nutrition and the use of other additives such as enzymes that can lead to beneficial effects on livestock performance. Enzymes are widely added to feeds for pigs and poultry, and these have contributed (with breeding) to the substantial gains in feed conversion efficiency that have been achieved.
What are the prospects for the future? For the mixed crop–livestock smallholder systems in developing countries, there may be places where these will intensify using the inputs and tools of high-input systems in the developed world. In the places where intensification of this nature will not be possible, there are many ways in which nutritional constraints could be addressed, based on what is locally acceptable and available. One area of high priority for additional exploration, which could potentially have broad implications for tropical ruminant nutrition, is microbial genomics of the rumen, building on current research into the breaking down of lignocellulose for biofuels (NRC 2009).
Addressing the nutritional constraints faced by pastoralists in extensive rangeland systems in the developing world is extremely difficult. While there is potential to improve livestock productivity in semi-arid and arid areas, probably the most feasible solutions require integrated application of what is already known, rather than new technology. This could involve dissemination of information from early warning systems and drought prediction, for example, so that herders can better manage the complex interactions between herd size, feed availability and rainfall (NRC 2009).
For the developed world, various drivers will shape the future of livestock nutrition. First, there is the continuing search for increased efficiency in livestock production. Margins for livestock farmers are likely to remain volatile and may be affected heavily by changes in energy prices, and increased feed conversion efficiency is one way to try to keep livestock production profitable. Public health issues will become increasingly important, such as concerns associated with the use of antibiotics in animal production, including microbiological hazards and residues in food (Vallat et al. 2005). The World Health Organization recommended that all subtherapeutic medical antibiotic use be stopped in livestock production in 1997, and proposed strict regulation and the phasing-out of other subtherapeutic treatments such as growth promotants; but appropriate surveillance and control programmes do not exist in many countries (Leakey et al. 2009). All antibiotics as growth promoters were banned in the European Union (EU) in 2006, but not all countries have made the same choice as the EU. Similarly, certain hormones can increase feed conversion efficiencies, particularly in cattle and pigs, and these are used in many parts of the world. The EU has also banned the use of hormones in livestock production. The globalization of the food supply chain will continue to raise consumer concerns for food safety and quality.
Another key driver that will affect livestock nutrition is the need (or in countries such as the UK, the legal obligation) to mitigate greenhouse gas emissions. Improved feeding practices (such as increased amounts of concentrates or improved pasture quality) can reduce methane emissions per kilogram of feed intake or per kilogram of product, although the magnitude of the latter reduction decreases as production increases. Many specific agents and dietary additives have been proposed to reduce methane emissions, including certain antibiotics, compounds that inhibit methanogenic bacteria, probiotics such as yeast culture and propionate precursors such as fumarate or malate that can reduce methane formation (Smith et al. 2007). Whether these various agents and additives are viable for practical use or not, and what their ultimate impacts could be on greenhouse gas mitigation, are areas that need further research.
Animal diseases generate a wide range of biophysical and socio-economic impacts that may be both direct and indirect, and may vary from localized to global (Perry & Sones 2009). The economic impacts of diseases are increasingly difficult to quantify, largely because of the complexity of the effects that they may have, but they may be enormous: the total costs of foot-and-mouth disease in the UK may have amounted to $18–25 billion between 1999 and 2002 (Bio-Era 2008).
The last few decades have seen a general reduction in the burden of livestock diseases, as a result of more effective drugs and vaccines and improvements in diagnostic technologies and services (Perry & Sones 2009). At the same time, new diseases have emerged, such as avian influenza H5N1, which have caused considerable global concern about the potential for a change in host species from poultry to man and an emerging global pandemic of human influenza.
In the developing world, there have been relatively few changes in the distribution, prevalence and impact of many epidemic and endemic diseases of livestock over the last two decades, particularly in Africa (Perry & Sones 2009), with a few exceptions such as the global eradication of rinderpest. Over this time, there has also been a general decline in the quality of veterinary services. A difficulty in assessing the changing disease status in much of the developing world is the lack of data, a critical area where progress needs to be made if disease diagnostics, monitoring and impact assessment are to be made effective and sustainable. Globally, the direct impacts of livestock diseases are decreasing, but the total impacts may actually be increasing, because in a globalized and highly interconnected world, the effects of disease extend far beyond animal sickness and mortality (Perry & Sones 2009).
For the future, the infectious disease threat will remain diverse and dynamic, and combating the emergence of completely unexpected diseases will require detection systems that are flexible and adaptable in the face of change (King et al. 2006b). Travel, migration and trade will all continue to promote the spread of infections into new populations. Trade in exotic species and in bush meat are likely to be increasing causes of concern, along with large-scale industrial production systems, in which conditions may be highly suitable for enabling disease transmission between animals and over large distances (Otte et al. 2007).
Over the long term, future disease trends could be heavily modified by climate change. For some vector-borne diseases such as malaria, trypanosomiasis and bluetongue, climate change may shift the geographical areas where the climate is suitable for the vector, but these shifts are not generally anticipated to be major over the next 20 years: other factors may have much more impact on shifting vector distributions in the short term (Woolhouse 2006). Even so, Van Dijk et al. (2010) have found evidence that climate change, especially elevated temperature, has already changed the overall abundance, seasonality and spatial spread of endemic helminths in the UK. This has obvious implications for policy-makers and the sheep and cattle industries, and raises the need for improved diagnosis and early detection of livestock parasitic disease, along with greatly increased awareness and preparedness to deal with disease patterns that are manifestly changing.
Climate change may have impacts not only on the distribution of disease vectors. Some diseases are associated with water, which may be exacerbated by flooding and complicated by inadequate water access. Droughts may force people and their livestock to move, potentially exposing them to environments with health risks to which they have not previously been exposed. While the direct impacts of climate change on livestock disease over the next two to three decades may be relatively muted (King et al. 2006b), there are considerable gaps in knowledge concerning many existing diseases of livestock and their relation to environmental factors, including climate.
Future disease trends are likely to be heavily modified by disease surveillance and control technologies. Potentially effective control measures already exist for many infectious diseases, and whether these are implemented appropriately could have considerable impacts on future disease trends. Recent years have seen considerable advances in the technology that can be brought to bear against disease, including DNA fingerprinting for surveillance, polymerase chain reaction tests for diagnostics and understanding resistance, genome sequencing and antiviral drugs (Perry & Sones 2009). There are also options associated with the manipulation of animal genetic resources, such as cross-breeding to introduce genes into breeds that are otherwise well-adapted to the required purposes, and the selection via molecular genetic markers of individuals with high levels of disease resistance or tolerance.
The future infectious disease situation is going to be different from today's (Woolhouse 2006), and will reflect many changes, including changes in mean climate and climate variability, demographic change and different technologies for combating infectious diseases. The nature of most, if not all, of these changes is uncertain, however.
4. Possible modifiers of future livestock production and consumption trends
(a) Competition for resources
Recent assessments expect little increase in pasture land (Bruinsma 2003; MA 2005). Some intensification in production is likely to occur in the humid–subhumid zones on the most suitable land, where this is feasible, through the use of improved pastures and effective management. In the more arid–semiarid areas, livestock are a key mechanism for managing risk, but population increases are fragmenting rangelands in many places, making it increasingly difficult for pastoralists to gain access to the feed and water resources that they have traditionally been able to access. In the future, grazing systems will increasingly provide ecosystem goods and services that are traded, but how future livestock production from these systems may be affected is not clear. The mixed crop–livestock systems will continue to be critical to future food security, as two-thirds of the global population live in these systems. Some of the higher potential mixed systems in Africa and Asia are already facing resource pressures, but there are various responses possible, including efficiency gains and intensification options (Herrero et al. 2010). Increasing competition for land in the future will also come from biofuels, driven by continued concerns about climate change, energy security and alternative income sources for agricultural households. Future scenarios of bioenergy use vary widely (Van Vuuren et al. 2009), and there are large evidence gaps concerning the likely trade-offs between food, feed and fuel in production systems in both developed and developing countries, particularly related to second-generation bioenergy technology.
Globally, freshwater resources are relatively scarce, amounting to only 2.5 per cent of all water resources (MA 2005). Groundwater also plays an important role in water supply: between 1.5 and 3 billion people depend on groundwater for drinking, and in some regions water tables are declining unremittingly (Rodell et al. 2009). By 2025, 64 per cent of the world's population will live in water-stressed basins, compared with 38 per cent today (Rosegrant et al. 2002). Increasing livestock numbers in the future will clearly add to the demand for water, particularly in the production of livestock feed: one cubic metre of water can produce anything from about 0.5 kg of dry animal feed in North American grasslands to about 5 kg of feed in some tropical systems (Peden et al. 2007). Several entry points for improving global livestock water productivity exist, such as increased use of crop residues and by-products, managing the spatial and temporal distribution of feed resources so as to better match availability with demand and managing systems so as to conserve water resources (Peden et al. 2007). More research is needed related to livestock–water interactions and integrated site-specific interventions, to ensure that livestock production in the future contributes to sustainable and productive use of water resources (Peden et al. 2007).
(b) Climate change
Climate change may have substantial effects on the global livestock sector. Livestock production systems will be affected in various ways (table 2 and see Thornton et al. (2009) for a review), and changes in productivity are inevitable. Increasing climate variability will undoubtedly increase livestock production risks as well as reduce the ability of farmers to manage these risks. At the same time, livestock food chains are major contributors to greenhouse gas emissions, accounting for perhaps 18 per cent of total anthropogenic emissions (Steinfeld et al. 2006). Offering relatively fewer cost-effective options than other sectors such as energy, transport and buildings, agriculture has not yet been a major player in the reduction of greenhouse gas emissions. This will change in the future (UNFCCC 2008), although guidance will be needed from rigorous analysis; for example, livestock consumption patterns in one country are often associated with land-use changes in other countries, and these have to be included in national greenhouse gas accounting exercises (Audsley et al. 2009).
Climate change will have severely deleterious impacts in many parts of the tropics and subtropics, even for small increases in the average temperature. This is in contrast to many parts of the temperate zone; at mid- to high latitudes, agricultural productivity is likely to increase slightly for local mean temperature increases of 1–3°C (IPCC 2007). There is a burgeoning literature on adaptation options, including new ways of using weather information to assist rural communities in managing the risks associated with rainfall variability and the design and piloting of livestock insurance schemes that are weather-indexed (Mude 2009). Many factors determine whether specific adaptation options are viable in particular locations. More extensive adaptation than is currently occurring is needed to reduce vulnerability to future climate change, and adaptation has barriers, limits and costs (IPCC 2007).
Similarly, there is a burgeoning literature on mitigation in agriculture. There are several options related to livestock, including grazing management and manure management. Global agriculture could offset 5–14% (with a potential maximum of 20%) of total annual CO2 emissions for prices ranging from $20 to 100 per t CO2 eq (Smith et al. 2008). Of this total, the mitigation potential of various strategies for the land-based livestock systems in the tropics amounts to about 4 per cent of the global agricultural mitigation potential to 2030 (Thornton & Herrero submitted), which could still be worth of the order of $1.3 billion per year at a price of $20 per t CO2 eq. Several of these mitigation options also have adaptive benefits, such as growing agroforestry species that can sequester carbon, which can also provide high-quality dietary supplements for cattle. Such carbon payments could represent a relatively large amount of potential income for resource-poor livestock keepers in the tropics. In the more intensive systems, progress could be made in mitigating GHG emissions from the livestock sector via increases in the efficiency of production using available technology, for the most part, and this may involve some shifting towards monogastric species.
(c) Socio-cultural modifiers
Social and cultural drivers of change are having profound effects on livestock systems in particular places, although it is often unclear how these drivers play out in relation to impacts on livestock and livestock systems. Livestock have multiple roles in human society. They contribute substantially and directly to food security and to human health. For poor and under-nourished people, particularly children, the addition of modest amounts of livestock products to their diets can have substantial benefits for physical and mental health (Neumann et al. 2003).
Livestock's contribution to livelihoods, particularly those of the poor in developing countries, is also well recognized. Livestock generate income by providing both food and non-food products that the household can sell in formal or informal markets. Non-food products such as wool, hides and skins are important sources of income in some regions: wool production in the high-altitude tropical regions of Bolivia, Peru or Nepal, for example. Hides and skins from home-slaughtered animals are rarely processed, as the returns may not justify the costs involved (Otte & Upton 2005). Livestock acquisition as a pathway out of poverty has been documented by Kristjanson et al. (2004) in western Kenya, for example. Livestock provide traction mainly in irrigated, densely populated areas, and allow cropping in these places. They provide nutrients in the form of manure, a key resource particularly for the mixed systems of sub-Saharan Africa. Livestock also serve as financial instruments, by providing households with an alternative for storing savings or accumulated capital, and they can be sold and transformed into cash as needed and so also provide an instrument of liquidity, consumption smoothing and insurance. For some poorer households, livestock can provide a means of income diversification to help deal with times of stress.
In addition to their food security, human health, economic and environmental roles, livestock have important social and cultural roles. In many parts of Africa, social relationships are partly defined in relation to livestock, and the size of a household's livestock holding may confer considerable social importance on it. The sharing of livestock with others is often a means to create or strengthen social relationships, through their use as dowry or bride price, as allocations to other family members and as loans (Kitalyi et al. 2005). Social status in livestock-based communities is often associated with leadership and access to (and authority over) natural, physical and financial resources.
Livestock may have considerable cultural value in developed countries also. Local breeds have often been the drivers of specific physical landscapes (e.g. extensive pig farming in the Mediterranean oak forests of the Iberian peninsula); as such, local breeds can be seen as critical elements of cultural networks (Gandini & Villa 2003).
Compared with the biophysical environment, the social and cultural contexts of livestock and livestock production are probably not that well understood, but these contexts are changing markedly in some places. External pressures are being brought to bear on traditional open-access grazing lands in southern Kenya, for example, such as increasing population density and increasing livestock–wildlife competition for scarce resources. At the same time, many Maasai feel that there is no option but to go along with subdivision, a process that is already well under way in many parts of the region, because they see it as the only way in which they can gain secure tenure of their land and water, even though they themselves are well aware that subdivision is likely to harm their long-term interests and wellbeing (Reid et al. 2008). There are thus considerable pressures on Maasai communities and societies, as many households become more connected to the cash economy, access to key grazing resources becomes increasingly problematic, and cultural and kinship networks that have supported them in the past increasingly feel the strain. Inevitably, the cultural and social roles of livestock will continue to change, and many of the resultant impacts on livelihoods and food security may not be positive.
Social and cultural changes are likewise taking place elsewhere. In European agriculture, there is already heightened emphasis on, and economic support for, the production of ecosystems goods and services, and this will undoubtedly increase in the future (Deuffic & Candau 2006). In the uplands of the UK, recent social changes have seen increasing demand for leisure provision and access to rural areas. At the same time, there are increasing pressures on the social functions and networks associated with the traditional farming systems of these areas, which have high cultural heritage value and considerable potential to supply the public goods that society is likely to demand in the future (Burton et al. 2005).
(d) Ethical concerns as a driver of change
Ethical concerns may play an increasing role in affecting the production and consumption of livestock products. Recent high-profile calls to flock to the banner of global vegetarianism, backed by exaggerated claims of livestock's role in anthropogenic global greenhouse gas emissions, serve mostly to highlight the need for rigorous analysis and credible numbers that can help inform public debate about these issues: there is much work to do in this area.
But science has already had a considerable impact on some ethical issues. Research into animal behaviour has provided evidence of animals' motivations and their mental capacities, which by extension provides strong support for the notion of animal sentience (i.e. animals' capacity to sense and feel), which in turn has provided the basis for EU and UK legislation that enshrines the concept of animal sentience in law (Lawrence 2009). Recently, European government strategies are tending to move away from legislation as the major mechanism for fostering animal welfare improvements to a greater concentration on collective action on behalf of all parties with interests in animal welfare, including consumers (Lawrence 2008). There is conflicting evidence as to the potential for adding value to animal products through higher welfare standards. There are common questions regarding the robustness of consumers' preferences regarding welfare-branded, organic and local food, for example, particularly in times of considerable economic uncertainty.
While there are differences between different countries in relation to animal welfare legislation, animal welfare is an increasingly global concern. Part of this probably arises as a result of the forces of globalization and international trade, but in many developing countries the roots of animal welfare may be different and relate more to the value that livestock have to different societies: the sole or major source of livelihood (in some marginal environments in SSA, for example), the organizing principle of society and culture (the Maasai, for instance), investment and insurance vehicles and sources of food, traction and manure, for example (Kitalyi et al. 2005).
Improving animal welfare need not penalize business returns and indeed may increase profits. For instance (and as noted above), measurements of functional traits indicate that focusing on breeding dairy cows for milk yield alone is unfavourably correlated with reductions in fertility and health traits (Lawrence et al. 2004). The most profitable bulls are those that produce daughters that yield rather less milk but are healthier and longer lived: the costs of producing less milk can be more than matched by the benefits of decreased health costs and a lower herd replacement rate. Identifying situations where animal welfare can be increased along with profits, and quantifying these trade-offs, requires integrated assessment frameworks that can handle the various and often complex inter-relationships between animal welfare, management and performance (Lawrence & Stott 2009).
(e) Wildcard drivers of change
There is considerable uncertainty related to technological development and to social and cultural change. This section briefly outlines an arbitrary selection of wildcards, developments that could have enormous implications for the livestock sector globally, either negatively (highly disruptive) or positively (highly beneficial).
(i) Artificial meat (more correctly, in vitro meat)
From a technological point of view, this may not be a wildcard at all, as its development is generally held to be perfectly feasible (Cuhls 2008), and indeed research projects on it have been running for a decade already. There are likely to be some issues associated with social acceptability, although presumably meat ‘grown in vats’ could be made healthier by changing its composition and made much more hygienic than traditional meat, as it would be cultured in sterile conditions. In vitro meat could potentially bypass many of the public health issues that are currently associated with livestock-based meat. The development and uptake of in vitro meat on a large scale would unquestionably be hugely disruptive to the traditional livestock sector. It would raise critical issues regarding livestock keeping and livelihoods of the resource-poor in many developing countries, for example. On the other hand, massive reductions in livestock numbers could contribute substantially to the reduction of greenhouse gases, although the net effects would depend on the resources needed to produce in vitro meat. There are many issues that would need to be considered, including the effects on rangelands of substantial decreases in the number of domesticated grazing animals, and some of the environmental and socio-cultural impacts would not be positive. There could also be impacts on the amenity value of landscapes with no livestock in some places. Commercial in vitro meat production is not likely to happen any time soon, however: at least another decade of research is needed, and then there will still be the challenges of scale and cost to be overcome.
This refers to an extremely dynamic field of research and application associated with particles of 1–100 nm in size (the size range of many molecules). Some particles of this size have peculiar physical and chemical properties, and it is such peculiarities that nanotechnology seeks to exploit. Nanotechnology is a highly diverse field, and includes extensions of conventional device physics, completely new approaches based upon molecular self-assembly and the development of new materials with nanoscale dimensions. There is even speculation as to whether matter can be directly controlled at the atomic scale. Some food and nutrition products containing nanoscale additives are already commercially available, and nanotechnology is in widespread use in advanced agrichemicals and agrichemical application systems (Brunori et al. 2008). The next few decades may well see nanotechnology applied to various areas in animal management. Nanosized, multipurpose sensors are already being developed that can report on the physiological status of animals, and advances can be expected in drug delivery methods using nanotubes and other nanoparticles that can be precisely targeted. Nanoparticles may be able to affect nutrient uptake and induce more efficient utilization of nutrients for milk production, for example. One possible approach to animal waste management involves adding nanoparticles to manure to enhance biogas production from anaerobic digesters or to reduce odours (Scott 2006). There are, however, considerable uncertainties concerning the possible human health and environmental impacts of nanoparticles, and these risks will have to be addressed by regulation and legislation: at present, for all practical purposes, nanotechnology is unregulated (Speiser 2008). Brunori et al. (2008) see nanotechnology as potentially a highly disruptive driver, and the ongoing debate as to the pros and cons is currently not well informed by objective information on the risks involved: much more information is required on its long-term impacts. Nanotechnology could redefine the entire notion of agriculture and many other human activities (Cuhls 2008).
(iii) Deepening social concerns about specific technology
Much evidence points to a serious disconnect between science and public perceptions. Marked distrust of science is a recurring theme in polls of public perceptions of nuclear energy, genetic modification and, spectacularly, anthropogenic global warming. One of several key reasons for this distrust is a lack of credible, transparent and well-communicated risk analyses associated with many of the highly technological issues of the day. This lack was noted above in relation to nanotechnology, but it applies in many other areas as well. The tools of science will be critical for bringing about food security and wellbeing for a global population of more than nine billion people in 2050 in the face of enormous technological, climatic and social challenges. Technology is necessary for the radical redirection of global food systems that many believe is inevitable, but technology alone is not sufficient: the context has to be provided whereby technology can build knowledge, networks and capacity (Kiers et al. 2008). One area where there are numerous potential applications to agriculture is the use of transgenic methodology to develop new or altered strains of livestock. These applications include ‘… improved milk production and composition, increased growth rate, improved feed usage, improved carcass composition, increased disease resistance, enhanced reproductive performance, and increased prolificacy’ (Wheeler 2007, p. 204). Social concerns could seriously jeopardize even the judicious application of such new science and technology in providing enormous economic, environmental and social benefits. If this is to be avoided, technology innovation has to take fully into account the health and environmental risks to which new technology may give rise. Serious and rapid attention needs to be given to risk analysis and communications policy.
What is the future for livestock systems globally? Several assessments agree that increases in the demand for livestock products, driven largely by human population growth, income growth and urbanization, will continue for the next three decades at least. Globally, increases in livestock productivity in the recent past have been driven mostly by animal science and technology, and scientific and technological developments in breeding, nutrition and animal health will continue to contribute to increasing potential production and further efficiency and genetic gains. Demand for livestock products in the future, particularly in developed countries, could be heavily moderated by socio-economic factors such as human health concerns and changing socio-cultural values.
In the future, livestock production is likely to be increasingly characterized by differences between developed and developing countries, and between highly intensive production systems on the one hand and smallholder and agropastoral systems on the other. How the various driving forces will play out in different regions of the world in the coming decades is highly uncertain, however. Of the many uncertainties, two seem over-arching. First, can future demand for livestock products be met through sustainable intensification in a carbon-constrained economy? Some indications have been given above of the increasing pressures on natural resources such as water and land; the increasing demand for livestock products will give rise to considerable competition for land between food and feed production; increasing industrialization of livestock production may lead to challenging problems of pollution of air and water; the biggest impacts of climate change are going to be seen in livestock and mixed systems in developing countries where people are already highly vulnerable; the need to adapt to climate change and to mitigate greenhouse emissions will undoubtedly add to the costs of production in different places; and the projected growth in biofuels may have substantial additional impacts on competition for land and on food security.
A second over-arching uncertainty is, will future livestock production have poverty alleviation benefits? The industrialization of livestock production in many parts of the world, both developed and developing, is either complete or continuing apace. The increasing demand for livestock products continues to be a key opportunity for poverty reduction and economic growth, although the evidence of the last 10 years suggests that only a few countries have taken advantage of this opportunity effectively (Dijkman 2009). Gura (2008) documents many cases where the poor have been disadvantaged by the industrialization of livestock production in developing countries, as well as highlighting the problems and inadequacies of commercial, industrial breeding lines, once all the functions of local breeds are genuinely taken into account. The future role of smallholders in global food production and food security in the coming decades is unclear. Smallholders currently are critical to food security for the vast majority of the poor, and this role is not likely to change significantly in the future, particularly in SSA. But increasing industrialization of livestock production may mean that smallholders continue to miss out on the undoubted opportunities that exist. There is no lack of suggestions as to what is needed to promote the development of sustainable and profitable smallholder livestock production: significant and sustained innovation in national and global livestock systems (Dijkman 2009); increasing regulation to govern contracts along food commodity chains, including acceptance and guarantee of collective rights and community control (Gura 2008); and building social protection and strengthening links to urban areas (Wiggins 2009). Probably all of these things are needed, headed by massive investment, particularly in Africa (World Bank 2009).
It is thought that humankind's association with domesticated animals goes back to around 10 000 BC, a history just about as long as our association with domesticated plants. What is in store for this association during the coming century is far from clear, although it is suffering stress and upheaval on several fronts. The global livestock sector may well undergo radical change in the future, but the association is still critical to the wellbeing of millions, possibly billions, of people: in many developing countries, at this stage in history, it has no known, viable substitute.
I am very grateful to the late Mike Gale and Maggie Gill for initiating this work and for advice, and to Michael Blummel, Phil Garnsworthy, Olivier Hanotte, Alistair Lawrence, Brian Perry, Wolfgang Ritter, Mark Rosegrant, Geoff Simm, Philip Skuce and Bill Thorpe, who all provided key inputs and information. Three anonymous reviewers provided helpful comments and suggestions on an earlier draft. Remaining errors and omissions are my responsibility entirely.
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