Animal husbandry is the branch of agriculture concerned with animals that are raised for meat, fibre, milk, eggs, or other products. It includes day-to-day care, selective breeding and the raising of livestock.
Husbandry has a long history, starting with the Neolithic revolution when animals were first domesticated, from around 13,000 BC onwards, antedating farming of the first crops. By the time of early civilisations such as ancient Egypt, cattle, sheep, goats and pigs were being raised on farms.
Major changes took place in the Columbian Exchange when Old World livestock were brought to the New World, and then in the British Agricultural Revolution of the 18th century, when livestock breeds like the Dishley Longhorn cattle and Lincoln Longwool sheep were rapidly improved by agriculturalists such as Robert Bakewell to yield more meat, milk, and wool.
A wide range of other species such as horse, water buffalo, llama, rabbit and guinea pig are used as livestock in some parts of the world. Insect farming, as well as aquaculture of fish, molluscs, and crustaceans, is widespread.
Modern animal husbandry relies on production systems adapted to the type of land available. Subsistence farming is being superseded by intensive animal farming in the more developed parts of the world, where for example beef cattle are kept in high density feedlots, and thousands of chickens may be raised in broiler houses or batteries. On poorer soil such as in uplands, animals are often kept more extensively, and may be allowed to roam widely, foraging for themselves.
Most livestock are herbivores, except for the pig which is an omnivore. Ruminants like cattle and sheep are adapted to feed on grass; they can forage outdoors, or may be fed entirely or in part on rations richer in energy and protein, such as pelleted cereals. Pigs and poultry cannot digest the cellulose in forage, and require cereals and other high-energy foods.
Husbandry, especially if it is intensive, has a substantial environmental impact, occupying about a third of the earth's ice-free land, causing loss of habitat and emitting about half of all greenhouse gas worldwide. Since the 18th century, people have become increasingly concerned about the welfare of farm animals, and laws and standards are widely enforced in response. In culture, animal husbandry often has an idyllic image, featuring in children's books and songs, where happy animals live in attractive countryside. A similar image may be projected by petting farms and by historic farms that offer farm-stays to paying visitors.
Further information: History of agriculture
Birth of husbandry
Main articles: Neolithic Revolution and Domestication of animals
The domestication of livestock was driven by the need to have food on hand when hunting was unproductive. The desirable characteristics of a domestic animal are that it should be useful to man, should be able to thrive in his company, should breed freely and be easy to tend.
Domestication was not a single event, but a process repeated at various periods in different places. Sheep and goats were the animals that accompanied the nomads in the Middle East, while cattle and pigs were associated with more settled communities.
The first wild animal to be domesticated was the dog. Half-wild dogs, perhaps starting with young individuals, may have been tolerated as scavengers and killers of vermin, and being naturally pack hunters, were predisposed to become part of the human pack and join in the hunt. Prey animals, sheep, goats, pigs and cattle, were progressively domesticated early in the history of agriculture.
Pigs were domesticated in Mesopotamia around 13,000 BC, and sheep followed, some time between 11,000 and 9,000 BC.Cattle were domesticated from the wild aurochs in the areas of modern Turkey and Pakistan around 8,500 BC.
A cow was a great advantage to a villager as she produced more milk than her calf needed, and her strength could be put to use, pulling a plough to increase production of crops, and drawing a sledge, and later a cart, to bring the produce home from the field. Draught animals were first used about 4,000 BC in the Middle East, increasing agricultural production immeasurably. In southern Asia, the elephant was domesticated by 6,000 BC.
Fossilised chicken bones dated to 5040 BC have been found in northeastern China, far from where their wild ancestors lived in the jungles of tropical Asia, but archaeologists believe that the original purpose of domestication was for the sport of cockfighting.
Meanwhile, in South America, the llama and the alpaca had been domesticated, probably before 3,000 BC, as beasts of burden and for their wool. Neither was strong enough to pull a plough which limited the development of agriculture in the New World.
Horses occur naturally on the steppes of Central Asia, and their domestication, around 3,000 BC in the Black Sea and Caspian Sea region, was originally as a source of meat; use as pack animals and for riding followed. Around the same time, the wild ass was being tamed in Egypt. Camels were domesticated soon after this, with the Bactrian camel in Mongolia and the Arabian camel becoming beasts of burden. By 1000 BC, caravans of Arabian camels were linking India with Mesopotamia and the Mediterranean.
In ancient Egypt, cattle were the most important livestock, and sheep, goats, and pigs were also kept; poultry including ducks, geese, and pigeons were captured in nets and bred on farms, where they were force-fed with dough to fatten them.
The Nile provided a plentiful source of fish. Honey bees were domesticated from at least the Old Kingdom, providing both honey and wax.
In ancient Rome, all the livestock known in ancient Egypt were available. In addition, rabbits were domesticated for food by the first century BC. To help flush them out from their underground burrows, the polecat was domesticated as the ferret, its use described by Pliny the Elder.
In northern Europe, agriculture including animal husbandry went into decline when the Roman empire collapsed. Some aspects such as the herding of animals continued throughout the period. By the 11th century, the economy had recovered and the countryside was again productive.
The Domesday Book recorded every parcel of land and every animal in Britain: "there was not one single hide, nor a yard of land, nay, moreover ... not even an ox, nor a cow, nor a swine was there left, that was not set down in [the king's] writ." For example, the royal manor of Earley in Berkshire, one of thousands of villages recorded in the book, had in 1086 "2 fisheries worth [paying tax of] 7s and 6d [each year] and 20 acres of meadow [for livestock]. Woodland for [feeding] 70 pigs."
The improvements of animal husbandry in the medieval period in Europe went hand in hand with other developments. Improvements to the plough allowed the soil to be tilled to a greater depth. Horses took over from oxen as the main providers of traction, new ideas on crop rotation were developed and the growing of crops for winter fodder gained ground. Peas, beans and vetches became common; they increased soil fertility through nitrogen fixation, allowing more livestock to be kept.
Main article: Columbian Exchange
Exploration and colonisation of North and South America resulted in the introduction into Europe of such crops as maize, potatoes, sweet potatoes and manioc, while the principal Old World livestock – cattle, horses, sheep and goats – were introduced into the New World for the first time along with wheat, barley, rice and turnips.
Main article: British Agricultural Revolution
Selective breeding for desired traits was established as a scientific practice by Robert Bakewell during the British Agricultural Revolution in the 18th century. One of his most important breeding programs was with sheep. Using native stock, he was able to quickly select for large, yet fine-boned sheep, with long, lustrous wool. The Lincoln Longwool was improved by Bakewell and in turn the Lincoln was used to develop the subsequent breed, named the New (or Dishley) Leicester. It was hornless and had a square, meaty body with straight top lines.
These sheep were exported widely and have contributed to numerous modern breeds. Under his influence, English farmers began to breed cattle for use primarily as beef. Long-horned heifers were crossed with the Westmoreland bull to create the Dishley Longhorn.
The semi-natural, unfertilized pastures formed by traditional agricultural methods in Europe were managed by grazing and mowing. As the ecological impact of this land management strategy is similar to the impact of such natural disturbances as a wildfire, this agricultural system shares many beneficial characteristics with a natural habitat, including the promotion of biodiversity. This strategy is declining in Europe today due to the intensification of agriculture. The mechanized and chemical methods used are causing biodiversity to decline.
Further information: Livestock
Further information: Agriculture § Livestock production systems, and Intensive animal farming
Traditionally, animal husbandry was part of the subsistence farmer's way of life, producing not only the food needed by the family but also the fuel, fertiliser, clothing, transport and draught power. Killing the animal for food was a secondary consideration, and wherever possible its products, such as wool, eggs, milk and blood (by the Maasai) were harvested while the animal was still alive.
In the traditional system of transhumance, people and livestock moved seasonally between fixed summer and winter pastures; in montane regions the summer pasture was up in the mountains, the winter pasture in the valleys.
Animals can be kept extensively or intensively. Extensive systems involve animals roaming at will, or under the supervision of a herdsman, often for their protection from predators. Ranching in the Western United States involves large herds of cattle grazing widely over public and private lands.
Similar cattle stations are found in South America, Australia and other places with large areas of land and low rainfall. Similar ranching systems have been used for sheep, deer, ostrich, emu, llama and alpaca.
In the uplands of the United Kingdom, sheep are turned out on the fells in spring and graze the abundant mountain grasses untended, being brought to lower altitudes late in the year, with supplementary feeding being provided in winter. In rural locations, pigs and poultry can obtain much of their nutrition from scavenging, and in African communities, hens may live for months without being fed, and still produce one or two eggs a week.
At the other extreme, in the more developed parts of the world, animals are often intensively managed; dairy cows may be kept in zero-grazing conditions with all their forage brought to them; beef cattle may be kept in high density feedlots; pigs may be housed in climate-controlled buildings and never go outdoors; poultry may be reared in barns and kept in cages as laying birds under lighting-controlled conditions. In between these two extremes are semi-intensive, often family run farms where livestock graze outside for much of the year, silage or hay is made to cover the times of year when the grass stops growing, and fertiliser, feed and other inputs are bought onto the farm from outside.
Main article: animal feed
Animals used as livestock are predominantly herbivorous, the main exception being the pig which is an omnivore. The herbivores can be divided into "concentrate selectors" which selectively feed on seeds, fruits and highly nutritious young foliage, "grazers" which mainly feed on grass, and "intermediate feeders" which choose their diet from the whole range of available plant material. Cattle, sheep, goats, deer and antelopes are ruminants; they digest food in two steps, chewing and swallowing in the normal way, and then regurgitating the semidigested cud to chew it again and thus extract the maximum possible food value.
The dietary needs of these animals is mostly met by eating grass. Grasses grow from the base of the leaf-blade, enabling it to thrive even when heavily grazed or cut.
In many climates grass growth is seasonal, for example in the temperate summer or tropical rainy season, so some areas of the crop are set aside to be cut and preserved, either as hay (dried grass), or as silage (fermented grass). Other forage crops are also grown and many of these, as well as crop residues, can be ensiled to fill the gap in the nutritional needs of livestock in the lean season.
Extensively reared animals may subsist entirely on forage, but more intensively kept livestock will require energy and protein-rich foods in addition. Energy is mainly derived from cereals and cereal by-products, fats and oils and sugar-rich foods, while protein may come from fish or meat meal, milk products, legumes and other plant foods, often the by-products of vegetable oil extraction.
Pigs and poultry are non-ruminants and unable to digest the cellulose in grass and other forages, so they are fed entirely on cereals and other high-energy foodstuffs. The ingredients for the animals' rations can be grown on the farm or can be bought, in the form of pelleted or cubed, compound foodstuffs specially formulated for the different classes of livestock, their growth stages and their specific nutritional requirements. Vitamins and minerals are added to balance the diet. Farmed fish are usually fed pelleted food.
Main article: Animal breeding
The breeding of farm animals seldom occurs spontaneously but is managed by farmers with a view to encouraging certain traits that are seen as desirable. These include hardiness, prolificness, mothering abilities, fast growth rates, low feed consumption per unit of growth, better body proportions, higher yields, better fibre qualities and other characteristics. Undesirable traits such as health defects, aggressiveness or lack of docility are selected against.
Selective breeding has been responsible for some large increases in productivity. In 2007, a typical broiler chicken at eight weeks old was 4.8 times as heavy as a bird of similar age in 1957. In the thirty years to 2007, the average milk yield of a dairy cow in the United States nearly doubled.
Techniques such as artificial insemination and embryo transfer are frequently used today, not only as methods to guarantee that females breed regularly but also to help improve herd genetics. This may be done by transplanting embryos from high-quality females into lower-quality surrogate mothers – freeing up the higher-quality mother to be reimpregnated. This practice vastly increases the number of offspring which may be produced by a small selection of the best quality parent animals.
On one hand, this improves the ability of the animals to convert feed to meat, milk, or fiber more efficiently, and improve the quality of the final product. On the other, it decreases genetic diversity, increasing the severity of certain disease outbreaks among other risks.
Further information: Veterinary medicine
Good husbandry, proper feeding, and hygiene are the main contributors to animal health on the farm, bringing economic benefits through maximised production. When, despite these precautions, animals still become sick, they are treated with veterinary medicines, by the farmer and the veterinarian. In the European Union, when farmers treat their own animals, they are required to follow the guidelines for treatment and to record the treatments given.
Animals are susceptible to a number of diseases and conditions that may affect their health. Some, like classical swine fever and scrapie are specific to one type of stock, while others, like foot-and-mouth disease affect all cloven-hoofed animals.
Where the condition is serious, governments impose regulations on import and export, on the movement of stock, quarantine restrictions and the reporting of suspected cases. Vaccines are available against certain diseases, and antibiotics are widely used where appropriate. At one time, antibiotics were routinely added to certain compound foodstuffs to promote growth, but this practice is now frowned on in many countries because of the risk that it may lead to antibiotic resistance.
Animals living under intensive conditions are particularly prone to internal and external parasites; increasing numbers of sea lice are affecting farmed salmon in Scotland. Reducing the parasite burdens of livestock results in increased productivity and profitability.
Governments are particularly concerned with zoonoses, diseases that humans may acquire from animals. Wild animal populations may harbour diseases that can affect domestic animals which may acquire them as a result of insufficient biosecurity. An outbreak of Nipah virus in Malaysia in 1999 was traced back to pigs becoming ill after contact with fruit-eating flying foxes, their faeces and urine. The pigs in turn passed the infection to humans. Avian flu H5N1 is present in wild bird populations and can be carried large distances by migrating birds. This virus is easily transmissible to domestic poultry, and to humans living in close proximity with them. Other infectious diseases affecting wild animals, farm animals and humans include rabies, leptospirosis, brucellosis, tuberculosis and trichinosis.
Range of species
Main articles: Livestock § Types, Aquaculture § Species groups, and Entomophagy
There is no single universally agreed definition of which species are livestock. Widely agreed types of livestock include cattle for beef and dairy, sheep, goats, pigs, and poultry. Various other species are sometimes considered livestock, such as horses, while poultry birds are sometimes excluded. In some parts of the world, livestock includes species such as buffalo, and the South American camelids, the alpaca and llama. Some authorities use much broader definitions to include fish in aquaculture, micro-livestock such as rabbits and guinea pigs, as well as insects from honey bees to crickets raised for human consumption.
Main article: Animal product
Animals are raised for a wide variety of products, principally meat, wool, milk, and eggs, but also including tallow, isinglass and rennet. Animals are also kept for more specialised purposes, such as to produce vaccines and antiserum (containing antibodies) for medical use. Where fodder or other crops are grown alongside animals, manure can serve as a fertiliser, returning minerals and organic matter to the soil in a semi-closed organic system.
Main article: Dairy farming
Although all mammals produce milk to nourish their young, the cow is predominantly used throughout the world to produce milk and milk products for human consumption. Other animals used to a lesser extent for this purpose include sheep, goats, camels, buffaloes, yaks, reindeer, horses and donkeys.
All these animals have been domesticated over the centuries, being bred for such desirable characteristics as fecundity, productivity, docility and the ability to thrive under the prevailing conditions. Whereas in the past, cattle had multiple functions, modern dairy cow breeding has resulted in specialised Holstein Friesian-type animals that produce large quantities of milk economically. Artificial insemination is widely available to allow farmers to select for the particular traits that suit their circumstances.
Whereas in the past, cows were kept in small herds on family farms, grazing pastures and being fed hay in winter, nowadays there is a trend towards larger herds, more intensive systems, the feeding of silage and "zero grazing", a system where grass is cut and brought to the cow, which is housed year-round.
In many communities, milk production is only part of the purpose of keeping an animal which may also be used as a beast of burden or to draw a plough, or for the production of fibre, meat and leather, with the dung being used for fuel or for the improvement of soil fertility. Sheep and goats may be favoured for dairy production in climates and conditions that do not suit dairy cows.
Main articles: Meat industry, Cattle, Sheep farming, and Pig farming
Meat, mainly from farmed animals, is a major source of dietary protein around the world, averaging about 8% of man's energy intake. The actual types eaten depend on local preferences, availability, cost and other factors, with cattle, sheep, pigs and goats being the main species involved. Cattle generally produce a single offspring annually which takes more than a year to mature; sheep and goats often have twins and these are ready for slaughter in less than a year; pigs are more prolific, producing more than one litter of up to about 11 piglets each year. Horses, donkeys, deer, buffalo, llamas, alpacas, guanacos and vicunas are farmed for meat in various regions. Some desirable traits of animals raised for meat include fecundity, hardiness, fast growth rate, ease of management and high food conversion efficiency. About half of the world's meat is produced from animals grazing on open ranges or on enclosed pastures, the other half being produced intensively in various factory-farming systems; these are mostly cows, pigs or poultry, and often reared indoors, typically at high densities.
Main article: Poultry farming
Poultry, kept for their eggs and for their meat, include chickens, turkeys, geese and ducks. The great majority of laying birds used for egg production are chickens. Methods for keeping layers range from free-range systems, where the birds can roam as they will but are housed at night for their own protection, through semi-intensive systems where they are housed in barns and have perches, litter and some freedom of movement, to intensive systems where they are kept in cages. The battery cages are arranged in long rows in multiple tiers, with external feeders, drinkers, and egg collection facilities. This is the most labour saving and economical method of egg production but has been criticised on animal welfare grounds as the birds are unable to exhibit their normal behaviours.
In the developed world, the majority of the poultry reared for meat is raised indoors in big sheds, with automated equipment under environmentally controlled conditions. Chickens raised in this way are known as broilers, and genetic improvements have meant that they can be grown to slaughter weight within six or seven weeks of hatching. Newly hatched chicks are restricted to a small area and given supplementary heating. Litter on the floor absorbs the droppings and the area occupied is expanded as they grow. Feed and water is supplied automatically and the lighting is controlled. The birds may be harvested on several occasions or the whole shed may be cleared at one time.
A similar rearing system is usually used for turkeys, which are less hardy than chickens, but they take longer to grow and are often moved on to separate fattening units to finish. Ducks are particularly popular in Asia and Australia and can be killed at seven weeks under commercial conditions.
Main article: Aquaculture
Aquaculture has been defined as "the farming of aquatic organisms including fish, molluscs, crustaceans and aquatic plants and implies some form of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc. Farming also implies individual or corporate ownership of the stock being cultivated." In practice it can take place in the sea or in freshwater, and be extensive or intensive. Whole bays, lakes or ponds may be devoted to aquaculture, or the farmed animal may be retained in cages (fish), artificial reefs, racks or strings (shellfish). Fish and prawns can be cultivated in rice paddies, either arriving naturally or being introduced, and both crops can be harvested together.
Fish hatcheries provide larval and juvenile fish, crustaceans and shellfish, for use in aquaculture systems. When large enough these are transferred to growing-on tanks and sold to fish farms to reach harvest size. Some species that are commonly raised in hatcheries include shrimps, prawns, salmon, tilapia, oysters and scallops. Similar facilities can be used to raise species with conservation needs to be released into the wild, or game fish for restocking waterways. Important aspects of husbandry at these early stages include selection of breeding stock, control of water quality and nutrition. In the wild, there is a massive amount of mortality at the nursery stage; farmers seek to minimise this while at the same time maximising growth rates.
Main articles: Beekeeping, Entomophagy, and Sericulture
Bees have been kept in hives since at least the First Dynasty of Egypt, five thousand years ago, and man had been harvesting honey from the wild long before that. Fixed comb hives are used in many parts of the world and are made from any locally available material. In more advanced economies, where modern strains of domestic bee have been selected for docility and productiveness, various designs of hive are used which enable the combs to be removed for processing and extraction of honey. Quite apart from the honey and wax they produce, honey bees are important pollinators of crops and wild plants, and in many places hives are transported around the countryside to assist in pollination.
Sericulture, the rearing of silkworms, was first adopted by the Chinese during the Shang dynasty. The only species farmed commercially is the domesticated silkmoth. When it spins its cocoon, each larva produces an exceedingly long, slender thread of silk. The larvae feed on mulberry leaves and in Europe, only one generation is normally raised each year as this is a deciduous tree. In China, Korea and Japan however, two generations are normal, and in the tropics, multiple generations are expected. Most production of silk occurs in the Far East, with a synthetic diet being used to rear the silkworms in Japan.
Insects form part of the human diet in some cultures, and in Thailand, crickets are farmed for this purpose in the north of the country and palm weevil larvae in the south. The crickets are kept in pens, boxes or drawers and fed on commercial pelleted poultry food, while the palm weevil larvae live on cabbage palm and sago palm trees, which limits their production to areas where these trees grow. Another delicacy of this region is the bamboo caterpillar, and the best rearing and harvesting techniques in semi-natural habitats are being studied.
Main articles: Environmental impact of livestock and Environmental impact of meat production
Animal husbandry has a significant impact on the world environment. It is responsible for somewhere between 20 and 33% of the fresh water usage in the world, and livestock, and the production of feed for them, occupy about a third of the earth's ice-free land. Livestock production is a contributing factor in species extinction, desertification, and habitat destruction. Animal agriculture contributes to species extinction in various ways. Habitat is destroyed by clearing forests and converting land to grow feed crops and for animal grazing, while predators and herbivores are frequently targeted and hunted because of a perceived threat to livestock profits; for example, animal husbandry is responsible for up to 91% of the deforestation in the Amazon region. In addition, livestock produce greenhouse gases. Cows produce some 570 million cubic metres of methane per day, that accounts for from 35 to 40% of the overall methane emissions of the planet. Livestock is responsible for 65% of all human-related emissions of the powerful and long-lived greenhouse gas nitrous oxide. As a result, ways of mitigating animal husbandry's environmental impact are being studied. Strategies include using biogas from manure.
Main article: Animal welfare
Since the 18th century, people have become increasingly concerned about the welfare of farm animals. Possible measures of welfare include longevity, behavior, physiology, reproduction, freedom from disease, and freedom from immunosuppression. Standards and laws for animal welfare have been created worldwide, broadly in line with the most widely held position in the western world, a form of utilitarianism: that it is morally acceptable for humans to use non-human animals, provided that no unnecessary suffering is caused, and that the benefits to humans outweigh the costs to the livestock. An opposing view is that animals have rights, should not be regarded as property, and should never be used by humans.
Since the 18th century, the farmer John Bull has represented English national identity, first in John Arbuthnot's political satires, and soon afterwards in cartoons by James Gillray and others including John Tenniel. He likes food, beer, dogs, horses, and country sports; he is practical and down to earth, and anti-intellectual.
Farm animals are widespread in books and songs for children; the reality of animal husbandry is often distorted, softened, or idealized, giving children an almost entirely fictitious account of farm life. The books often depict a rural idyll of happy animals free to roam in attractive countryside, which is completely at odds with the realities of the impersonal, mechanized activities involved in modern intensive farming.
Pigs, for example, appear in several of Beatrix Potter's "little books", as Piglet in A. A. Milne's Winnie the Pooh stories, and somewhat more darkly (with a hint of animals going to slaughter) as Babe in Dick King-Smith's The Sheep-Pig, and as Wilbur in Charlotte's Web. Pigs tend to be "bearers of cheerfulness, good humour and innocence". Many of these books are completely anthropomorphic, dressing farm animals in clothes and having them walk on two legs, live in houses, and perform human activities. The children's song "Old MacDonald Had a Farm" describes a farmer named MacDonald and the various animals he keeps, celebrating the noises they each make.
Many urban children experience animal husbandry for the first time at a petting farm; in Britain, some five million people a year visit a farm of some kind. This presents some risk of infection, especially if children handle animals and then fail to wash their hands; a strain of E. coliinfected 93 people who had visited an interactive farm in an outbreak in 2009. Historic farms offer farmstays and "a carefully curated version of farming to those willing to pay for it", sometimes giving visitors a romanticised image of a pastoral ideal from an unspecified time in the pre-industrial past.
- ^Clutton-Brock, Juliet (1999). A Natural History of Domesticated Mammals. Cambridge University Press. pp. 1–2. ISBN 978-0-521-63495-3.
- ^ abcde"History of the domestication of animals". Historyworld. Retrieved 3 June 2017.
- ^Nelson, Sarah M. (1998). Ancestors for the Pigs. Pigs in prehistory. University of Pennsylvania Museum of Archaeology and Anthropology.
- ^Ensminger, M.E.; Parker, R.O. (1986). Sheep and Goat Science (Fifth ed.). Interstate Printers and Publishers. ISBN 0-8134-2464-X.
- ^McTavish, E.J., Decker, J.E., Schnabel, R.D., Taylor, J.F. and Hillis, D.M. (2013). "New World cattle show ancestry from multiple independent domestication events". Proc. Natl. Acad. Sci. U.S.A. National Academy of Sciences. 110: 1398–1406. doi:10.1073/pnas.1303367110. PMC 3625352. PMID 23530234.
- ^Gupta, Anil K. in Origin of agriculture and domestication of plants and animals linked to early Holocene climate amelioration, Current Science, Vol. 87, No. 1, 10 July 2004 59. Indian Academy of Sciences.
- ^Adler, Jerry; Lawler, Andrew (1 June 2012). "How the Chicken Conquered the World". Smithsonian Magazine. Retrieved 5 June 2017.
- ^Sapir-Hen, Lidar; Erez Ben-Yosef (2013). "The Introduction of Domestic Camels to the Southern Levant: Evidence from the Aravah Valley"(PDF). Tel Aviv. 40: 277–85. doi:10.1179/033443513x13753505864089.
- ^Manuelian, Peter der (1998). Egypt: The World of the Pharaohs
- ^Both the name Bull and the reference to bacon indicate the archetypal livestock farmer.
If the scientist needs to contact the animal facility after any study to inquire about husbandry details, this represents a lost opportunity, which can ultimately interfere with the study results and their interpretation. There is a clear tendency for authors to describe methodological procedures down to the smallest detail, but at the same time to provide minimal information on animals and their husbandry. Controlling all major variables as far as possible is the key issue when establishing an experimental design. The other common mechanism affecting study results is a change in the variation. Factors causing bias or variation changes are also detectable within husbandry. Our lives and the lives of animals are governed by cycles: the seasons, the reproductive cycle, the weekend-working days, the cage change/room sanitation cycle, and the diurnal rhythm. Some of these may be attributable to routine husbandry, and the rest are cycles, which may be affected by husbandry procedures. Other issues to be considered are consequences of in-house transport, restrictions caused by caging, randomization of cage location, the physical environment inside the cage, the acoustic environment audible to animals, olfactory environment, materials in the cage, cage complexity, feeding regimens, kinship, and humans. Laboratory animal husbandry issues are an integral but underappreciated part of investigators' experimental design, which if ignored can cause major interference with the results. All researchers should familiarize themselves with the current routine animal care of the facility serving them, including their capabilities for the monitoring of biological and physicochemical environment.
animal husbandry, animal research, experimental design
If the scientist needs to contact the animal facility after the study is completed and inquire about husbandry details to be included in the manuscript, it is obvious that there has not been proper emphasis placed on animal husbandry-related issues in the experimental design. Unless agreed otherwise, all facilities follow their own animal care routines, which may not be suitable or include the best choices for individual studies. It may be possible to obtain information on this routine care afterwards, but study-specific details, e.g., when the cages were changed, the location of cages in the rack, and any aberrations in environment may no longer be available. This is an opportunity lost and can ultimately interfere with the study results and their interpretation. Contacts with the animal facility personnel to include and plan husbandry-related aspects should be established well ahead of the study.
An original article communicates results to the scientific community; therefore, it is absolutely necessary that the article contains a complete description of the study under comparable conditions, preferably following ARRIVE guidelines (Kilkenny et al. 2010) to help fellow scientists design future investigations. An article not revealing all the essential pieces of information becomes impossible to repeat with the same results, yet repeatability is one of the key qualities that all scientists seek. There is a clear tendency for researchers to describe procedures, chemicals, reagents, and statistics down to the smallest detail, yet at the same time provide minimal information on animals and their husbandry (Alfaro 2005; Everitt and Foster 2004; Gerdin et al. 2012).
The most common animal study type deals with interference with the natural order of events and carefully observing the consequences. The importance stems from the quest for inference, i.e., what is produced, contributed to, or caused without ambiguity. In the end, the authors must be able to rule out all possible alternate causes for the results they have obtained. Husbandry issues should be included as essential parts of this process.
There are several recent guidelines available to describe animals and their husbandry (Alfaro 2005; Brattelid and Smith 2000; Hooijmans et al. 2010; Kilkenny et al. 2010; National Research Council (US) Institute for Laboratory Animal Research 2011). Some are based on surveys of the existing situation, while others provide reasons or lists of items to be described. A closer look at the surveys assessing the quality of design reveals that there are common deficiencies in design, such as lack of description of randomization and bias (Kilkenny et al. 2009; McCance 1995; Perel et al. 2007). Although the primary focus of randomization is on random allocation of the animals to the groups, it is feasible to assume that the same deficiencies are true for husbandry-related experimental design items.
How Husbandry Variables Can Impact Study Outcome
Controlling all major variables as far as possible is the key issue when establishing an experimental design, i.e., the only difference between the study and control groups is the procedure and nothing else. Any remaining variation can be controlled by randomizing the treatments to the animals. This applies to all aspects of the design, e.g., procedures under study and everything influencing the lives of the animals and to what they are exposed.
Bias is any systematic difference between the groups in addition to the procedure in the study design. No one would purposely incorporate bias into their design, yet it may be introduced because several aspects have not been properly considered or understood or the possibility has been totally ignored. A simple example of a bias is a study examining the effects of ethanol on animals through offering 10% ethanol in the drinking water. In reality, this design evaluates the combined effects of ethanol, eating less, and drinking less; the latter because animals tend to drink less fluid and ethanol provides a considerable amount of calories and eating is calorie guided.
The other common mechanism affecting study results is a change in variation; sources of variation in animal study in relation to husbandry and beyond have been analyzed by Howard (2002). An increase in the background noise makes statistical significance more difficult to attain or it may require more animals. Consequently, a decrease in variation will have the opposite effect. Husbandry-related variation effects are traceable to disturbances in animals' lives, such as disease, transportation or cage change, or simply exposure to a fluctuating or changing physicochemical environment. In principle, a change in variation can be caused by any husbandry variable, though some are more likely candidates than others. While establishing an experimental design for an experiment, it is important to invest adequate time for the identification of such factors and building up effective strategies to cope with them. The aim of this paper is to elucidate selected animal housing and care-related items with examples and discuss their potential to interfere with the experimental design.
Animal life follows many different cycles, including the seasonal cycle, reproductive cycle, weekend-working days cycle, cage change /room sanitation cycle, and diurnal cycle. Some of these are actually established by the routine husbandry, and the rest are cycles that are sensitive to husbandry procedures.
Animals are capable of sensing the season even when housed in windowless rooms with programmed photoperiods and with a tightly regulated physicochemical environment. For example, there are reports of seasonal variation of immunoreactivity in models of septic shock and immunosuppression induced by chronic stress in 2 strains of mice. Kiank et al. (2007) showed that mice living with a 12:12-hour photoperiod had an enhanced risk to die of peritonitis in the summer or autumn compared with the other seasons. This is a situation where a control group may offer a solution to this problem. Theoretically, there is no other way to counteract seasonal variation other than to always carry out the study during the same season, yet even seasons are not alike and this approach as such may not be practical.
In rodents, the female reproductive cycle is sensitive to the pheromones present in male urine. Classical examples of this are the Whitten effect; male pheromones synchronizing estrus in females, the Lee–Boot effect; suppression or prolongation of estrous cycles of mature females when they are housed in groups and isolated from male mice, and the Bruce effect, which refers to the tendency for female rodents to terminate their pregnancies following exposure to the scent of an unfamiliar male.
Controlling spread of odors within a room, if not to the whole facility, is problematic; this is possible only if ventilation of the test enclosure is separated from the rest of the animals. In other situations, all persons visiting animal rooms should wash their hands with unscented soap and change protective clothing between the rooms (Wersinger and Martin 2009).
Weekend-Working Days Cycle
During the weekend, fewer people are present in the animal facility; there is less human activity and hence a reduced acoustic environment audible to animals in the animal rooms. This change does not go unnoticed by the animals. Whether this represents a better time window for sampling and recording is a study-specific question.
For instance, this cycle causes change in blood pressure, which is a parameter commonly recorded in research. By using telemetric methods, which allow continuous recording of freely moving animals, it has been shown that spontaneous locomotor activity and blood pressure in the working days in rats are higher than during weekends. Apart from the increased locomotor activity (33%, p < 0.001), the daytime blood pressure differences were small (3.7–4.2 mmHg, p < 0.05) yet large enough to complicate the interpretation of study results (Schreuder et al. 2007).
In most animal facilities, sound levels are low during the weekends, suggesting that human activities are a very important source of sound (Milligan et al. 1993). Every facility has its own weekend environment, and all weekends are not exact replicas of the previous ones. For the purposes of experimental design, this possible confounding effect has to be discussed with the facility personnel to decide whether to conduct samplings all through 7 days a week, or to use either working days or weekends, keeping in mind that there may be other disturbing factors that one may prefer to avoid.
Cage Change and Room Sanitation Cycle
Cage changes and room sanitation represent major exposures for laboratory animals. The key question here is how long the animals are disturbed and what is the magnitude and nature of the disturbance, starting from preparations and in particular after the cage change, when the animals are not suitable for sampling or recording. Another solution is to find and use appropriate husbandry procedures to replicate the previous physiological state.
Rats housed in their home cages display increased locomotive activity, bedding manipulation, and defecation in both the mornings and afternoons of cage change days. This behavioral effect is greater than that of time of day and lasts for several hours after the cage change (Saibaba et al. 1996). Likewise in rats, the cage change results in elevations in heart rate and mean arterial pressure levels lasting for up to 5 hours after the procedure. The reactions observed after cage change were significantly greater than those observed after simple handling, handling being part of the cage change process (Meller et al. 2011).
In mice, postcleaning activity also includes aggression, which can cause serious injuries (Van Loo et al. 2004). In C57BL6/NTac mice, the cage change increased systolic blood pressure, heart rate, and locomotor activity; in females, these changes lasted about 100 minutes, while in males the effect duration was about 20 to 25% shorter, irrespective of change frequency (weekly vs. fortnightly) (Gerdin et al. 2012). It seems safe to recommend that no manipulation, dosing, sampling, or recording of animals should be done during the cage change day or the following day. For sensitive behavioral experiments, an even longer timescale may be necessary.
In studies on social behavior, the routine frequency of cage cleaning can be deleterious by disrupting its environment, including scent marks (pheromones), nests, and hoarded food. Cage cleaning and sanitation processes can also alter a rodent's normal production of pheromones and thus may affect behavior. To prevent pheromonal interference and stress-induced pheromonal release in their research subjects, experimenters should assess their current laboratory protocols regarding cage cleaning processes, housing designs, and behavioral assays. The lowest possible frequency would avoid unnecessary stress to animals (Wersinger and Martin 2009).
There is evidence that transfer of specific olfactory cues during cage cleaning and the provision of nesting material can decrease aggression and stress in group-housed male mice (Van Loo et al. 2004). Removing only the wet soiled bedding from a dirty cage, returning the nest or a portion of soiled bedding, some familiar complexity item, or food hopper with diet to the clean cage might be better options for the animals and the study design (Bind et al. 2013; Meller et al. 2011; Wersinger and Martin 2009).
Diurnal rhythm influences many aspects of animal life, and changes seen are more than minute “physiologic” variations around a 24-hour mean. The rhythm has an endogenous nature but is affected by husbandry-related factors such as food, light, stress, and even tinted cage walls, and it also influences in vivo results such as melatonin, total fatty acids, glucose, lactic acid, corticosterone, insulin, and leptin in rats (Wren et al. 2014). In animal care and housing, one should avoid anything that could disrupt the diurnal rhythm, such as malfunctioning or changing photoperiods or practicing common types of restricted feeding (Chacon et al. 2005).
Ideally, samples and recordings should be obtained from freely moving animals, so that they are not aware of the procedure. In most cases, this simply is not possible; hence, samples are ‘contaminated’ with human presence in the room and the handling and sampling method. Moving the animals to another space gives them more time to react compared with the same procedure done in the animal room. For example, when cages of group-housed mice were transported to another room on a wheeled trolley and stored on a mobile ventilated rack during testing, this had no effect on blood glucose, but body temperature increased significantly when compared with nontransported controls. It required one hour of acclimatization for temperature to be restored (Gerdin et al. 2012). Because there are more and less sensitive parameters to be assessed in each study, the study group has to evaluate the optimal location to conduct the procedures.
Current caging systems have been designed primarily with disease control in mind, i.e., materials should be easy to sanitize and sterilize. Complexity items came later; some of them are intended only for single use, some can be used to transfer specific olfactory cues during cage cleaning. Any disease, whether overt or subclinical, can interfere with the investigation in an unpredictable way. Health monitoring is practiced to detect the presence of an animal pathogen as quickly as possible. Depending on the caging system, this may require measures ranging from decontamination of the entire facility to a few cages.
Protection of the animals against pathogenic organisms is crucial to animals, animal center personnel, and investigators. The facility has rules to be followed and obeyed, e.g., restricted access of both animals and humans into the facility, acceptable working practices when inside, and requirements for cleaning of research equipment, instruments, and biological materials, and these must be adhered to while establishing the experimental design.
The investigators should allocate the animals at random into the study groups, and then cages should be placed into the cage rack also at random. An alternative is to incorporate blocking, which would not involve an increase in the number of animals but might provide additional information on analysis. Cages in different locations experience temperature, humidity, and lighting gradients based on cage level, distance to ventilation inlets and exhausts, lighting, and even sound sources. If cages are assigned to cage racks in a systematic manner, these external factors can introduce bias into the statistical analyses. These kinds of effects have been reported, but it is likely that most of these biased results have gone unnoticed (Herzberg and Lagakos 1992).
Animal technicians should be told that cage locations are being randomized and be given the master key to the locations. Unless this is done, the location may accidentally change. There are claims that cage locations should be continuously changed, e.g., at each cage change and that would achieve the same goal as permanent random order. Unfortunately, this is not the case; instead, continuous place change leads to increased variation in parameters sensitive to gradients in the room.
Temperature Humidity and Illumination
All holding and caging systems do not provide similar environments to the animals. In some cages, the physical environment is close to the one in the room, whereas in others the changes can be considerable. As an example, a study by Memarzadeh et al. (2004) compared environmental conditions inside mice cages with 4 different mechanical ventilation designs and a static isolator cage. The static isolator cages were found to have lower air velocity, higher relative humidity, higher NH3 and CO2 levels, lower body weight gain, and lower water consumption compared with the mechanically ventilated cages (Memarzadeh et al. 2004). In mice, temperature and humidity variation can affect the age of puberty, i.e., low temperatures and extremely low humidity levels have been shown to delay sexual maturation (Drickamer 1990).
Illumination has been shown to affect the estrous cycle in both in albino and normally pigmented mice. When 2 light intensities (15–20 and 220–290 lux) were used, the estrous cycle of both types of mice was shorter, and the proportion of albino mice from which embryos were recovered was significantly smaller than the proportion from black mice at the lower intensity (Donnelly and Saibaba 1993).
Noise sources are facility specific and include environmental control systems, maintenance and husbandry procedures, cleaning equipment, and other equipment used near to the animals. The sounds cover a wide frequency range, including the ultrasonic ( >20 kHz) frequency that animals but not humans hear. It seems likely that the levels reported can have a negative effect on animal physiology or behavior (Sales et al. 1999). It is rather rare for the facilities to monitor the acoustic environment, especially ultrasounds beyond the range of human hearing. Although background sound levels in undisturbed situations are generally low, marked increases in sound levels often occur during the working days. It is clear that the acoustic environment of laboratory animals is an uncontrolled variable with the potential to interfere with behavioral and physiological experiments (Milligan et al. 1993).
Investigators cannot avoid noise created by HVAC machinery in the facility, but they can try to make best of it. A good starting point is to find out whether the facility has assessed the sounds audible to animals all the time and those created by machinery used intermittently, such as cage and rack washers and autoclaves. Avoiding cage manipulations such as cage change, addition of diet to the cage lid and topping off water bottles (Voipio et al. 2006), all sanitation processes, the presence of other experimenters in the same space, and conducting tests during the weekends are all things to be considered. If there are building construction activities causing noise or vibrations going on nearby, it may be best to avoid any studies at all.
Laboratory animals have a much better developed sense of smell than humans. Therefore, it is no surprise that the olfactory environment is important and any disruption to it carries wide range of consequences to the animals and hence to the study results. For example, changing the cage bedding and/or nesting material at various prescribed intervals results in delayed puberty as compared with nondisrupted control mice (Drickamer 1990). Open-top cages allow the odors to spread from one room to the next unless animals are housed in special conditions, e.g., in an IVC-system or isolators with separate inlet and exhaust air ducts.
Traditionally, the polymers used as cage materials have been considered as being inert. The most common clear material, polycarbonate, has been shown to leach Bisphenol A, a monomer with estrogenic activity. Howdeshell et al. (2003) have shown that this compound becomes a problem once polycarbonate equipment is exposed to high temperatures and alkaline conditions, common procedures in sterilization and washing, and the amount of leaching increases as a function of use. Bisphenol A exposure as a result of being housed in used polycarbonate cages produced a 16% increase in uterine weight in prepubertal female mice relative to females housed in used polypropylene cages; however, it has to be noted that this difference was not statistically significant (Howdeshell et al. 2003). This should be taken as a warning sign; the animals in old cages with bottles or even complexity items made of polycarbonate may be exposed to varying amounts of Bisphenol A, which may interfere with any estrogen-sensitive parameters. The only effective solution is to avoid using polycarbonate cages; other polymer materials are less prone to leaching of this chemical.
Bedding is the material with which the animals have continuous contact. The original observation that softwood bedding contains α- and β-pinene, which are compounds with liver microsomal enzyme induction properties, is quite old but so far it has not been widely implemented (Vesell 1967). This is not the only effect of bedding; several other interfering properties have subsequently been discovered, e.g., measurable amounts of endotoxin and (1– >3)-beta-d-glucan are present in different bedding materials; after 5 weeks' exposure, this evoked moderate inflammatory reactions in the lung of the animals (Ewaldsson et al. 2002).
To exclude bedding interference, one can assay residues in a batch, keep to one batch whenever possible, and, if using softwood bedding, then it is advisable to standardize heat treatments both at the manufacturer's plant and the facility, because heat treatment can decrease the levels of the compounds responsible for enzyme induction (Nevalainen and Vartiainen 1996).
Adding items and materials into the cage increases the complexity of the intimate environment of the animals. Complexity becomes environmental enrichment once it has been verified to confer a welfare outcome on the animals. However, despite many studies on complexity, there are still major gaps in our understanding, e.g., because of variety of item combinations, lack of applicability beyond one strain or stock of animals, and inappropriate controls.
For the scientist, the most important aspect of complexity is consistency; the added items must be present all of the time and they have to be the same for all animals. In group-housed animals, social hierarchies may influence the use of complexity items. Both the facility and the scientists need to understand that complexity is not an inert object in the cage but a potential variable in the study. Changing the intimate environment of animals has effects on brain structure, physiology, and behavior as well as an influence on which genes are expressed in various organs (Benefiel et al. 2005). It has to be understood that minor complexity changes meant to improve animal welfare may alter the physiology and development of the animals in an unpredictable way. Moreover, there is also the possibility that the complexity preferred by the animals may not enhance laboratory animal welfare and may even interfere with the study (Benefiel et al. 2005; Wersinger and Martin 2009). It is important to consider the potential effects of any complexity on welfare of the animal strain in use and, even more importantly, more studies need to be done to obtain more accurate data.
Variability between diet brands is to be expected, but there may be considerable variation between batches of the same diet brand. Consequently, the study parameters will also vary. Keeping to one batch in an experiment is advisable, but in subsequent studies, this may not be possible, and then analysis of at least the critical components affecting the study may be helpful. Because the food deteriorates during storage, the analysis may also be necessary if the duration of the experiment is prolonged.
It is widely known that eating too much is unhealthy, but this is what we routinely offer to our research animals. The drawbacks of ad libitum feeding include an increased variation in food intake and consequently an increased variation in body weight and other variables and increased mortality and shorter lifespan. It is not surprising that ad libitum feeding has been called the least controlled variable in rodent bioassays (Keenan et al. 1998).
Dietary restriction is the solution to these problems, but this can lead to other problems. Dietary restriction in rodents requires single housing in order to provide them with a meal once a day, often during the daytime; this disrupts physiological and behavioral diurnal rhythms and would exert a confounding effect on the investigation (Chacon et al. 2005; Damiola et al. 2000; Forestell et al. 2001; Nelson 1988). For example, in studies with dietary restriction, it is unclear whether the differences observed are due to caloric intake per se or altered diurnal rhythms.
The diet board offers the possibility of combining dietary restriction with group-housing and normal eating rhythms (Kasanen et al. 2009a, 2009b). From the point of view of scientific quality, the combination of undisturbed diurnal rhythm and restricted caloric intake in rodents would be a valuable achievement. In rats fed with the diet board, serum ghrelin, blood glucose, and fecal corticosterone and immunoglobulin A have been shown to follow a diurnal rhythm (Kasanen et al. 2010).
Scientists are well aware that with large laboratory animals, family relationship such as sisters and brothers must be evenly distributed to all groups in the study. The same allocation principle is not practiced with small laboratory animals, such as rodents. Although rats and mice look alike and litter data is usually lost at weaning, when the sexes are separated and cages filled to predetermined cage occupancy, nonetheless this may not be the best practice.
Good laboratory practice-guidelines emphasize that the study design should take account of kinship in large animals, but not for rodents. Safety studies with small animals typically include hundreds of animals, whereas in studies with large animals, the numbers are comparable with the numbers of small animals used in basic biomedical research. Rather than tacitly accepting the difference in scale of experimental design, it is worth noticing that it is often logically inconsistent. Indeed, this a question of animal numbers, not of species.
In outbred and other undefined animals, litter effects are large and ignoring them can make replication of the studies difficult, if not impossible. As an example, a recent literature review of the valproic acid model of autism showed that only 9% (3/34) of studies correctly determined that the experimental unit was the litter and therefore had made valid statistical inferences. In fact, litter effects accounted for up to 61% (p < 0.001) of the variation in behavioral outcomes, a much larger percentage than the treatment effects (Lazic and Essioux 2013).
The need to recognize kinship is clear with outbred animals, but it should not be ignored in inbred and defined animals. Prager et al. (2010) showed that in young outbred rats, maternal care and litter size exerted a profound effect on immune-related parameters. Although inbred animals are genetically identical, their embryonic development and maternal care may not be the same, and hence kinship is an issue to be considered with defined strains of laboratory animals.
Accounting for kinship in rodents becomes a reality only once litter codes are available. In the case of in-house breeding, this should not be too difficult. With major breeders, this must be possible but ordering has to be done earlier than usual. The expected higher cost of animals can be offset by a reduction in the numbers of animals needed and thus less labor. When kinship data are available, animals should be divided into the study groups as evenly as possible following a random block design as presented by Festing et al. (2002).
Animal technicians, not only the scientists, should be considered as key individuals in the studies. The technicians see and observe the animals at least on a daily basis and consequently have a good understanding of what is normal in these animals and in particular what is not. They are also in charge of daily routines, and the way they deal with the animals can make a profound difference.
There is anecdotal evidence that if rats are moved to a new cage by lifting from the base of the tail, they become aggressive, and that this does not happen if they are lifted by holding the body. Lifting by the base of tail has traditionally been the preferred method for mice, and these animals have been considered aggressive and they do not habituate to handling. A recent article by Hurst and West (2010) has challenged this view using 2 strains and a stock of mice. If the mice were transferred to a new cage in cupped hands or in a transparent tunnel kept in the cage, then their anxiety decreased already after one such transfer. The animals were more tame when receiving administrations using the traditional means of immobilization (Hurst and West 2010).
It was concluded that there is no need to consider handling-induced anxiety in mice, in essence representing an animal model of anxiety (Hurst and West 2010). Investigators are urged to find out the advice provided by the facility on how to handle animals during routine care. Furthermore, they may apply this approach themselves and see the outcome.
Laboratory animal husbandry issues are an integral but underappreciated part of experimental design, which if ignored can cause major interference with the results. All study groups should familiarize themselves with the current routine animal care of the facility serving them and their monitoring capabilities on biological and physicochemical environment. With respect to husbandry issues, it is often easier to say what should not be done rather than what to do, but the final decisions are left to the group and depend largely on specific requirements of the study. While defining the experimental design for an experiment, it is important to invest adequate time in the identification of such issues and to devise effective strategies to deal with them.
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