Chapter 14
Production (Farm) Animals
Production animals are those that are farmed to produce food for human consumption (meat, milk, eggs), or animal by-products (wool, fibre, hides). They include a number of domestic ungulates (sheep, goats, pigs and cattle), as well as several species of poultry and some farmed fish.
Farm animals have several disadvantages as research tools when compared with the more common laboratory animal species. They are generally outbred populations, with many different breeds and cross-breeds and the majority of them have a poorly defined health status. All of the ungulate species have gestation periods measured in months, rather than days, and, with the exception of pigs, they also have very small litter sizes. These factors can make it extremely difficult to source large numbers of healthy farm animals that are matched for breed, sex and age.
In 2010, farm animals accounted for 5% of the 3.7 million procedures started that year in the UK1. The majority of these were poultry species (133 000), with smaller numbers of sheep (38 000), pigs (2700), cattle (2100) and other ungulates (100).
Poultry
Poultry is a generic term used to describe birds that are kept for meat or egg production. The predominant species of poultry is the domestic chicken, but the term also includes turkeys, ducks, geese, bantams, partridges, quail, pheasants, guinea fowl, ostriches, emus, rheas and pigeons.
In 2010, domestic chickens accounted for 91.5% of all the procedures carried out using avian species in the UK1. Many viruses are propagated in embryonated chicken eggs; for example, influenza viruses. Turkeys were used in a further 1.8%, whereas quail, ducks and geese (both domestic and wild), pigeons and the red jungle fowl accounted for only small numbers. Other non-poultry birds (finches, tits, starlings, crows, wild seabirds and the pied flycatcher) made up the remaining 6%. A simple classification of the majority of birds used in research is given in Figure 14.1.
Figure 14.1 Classification of birds.
| Class | Order | Species |
| Aves | Galliformes | Domestic chicken (Gallus gallus domesticus) |
| Domestic turkey (Meleagris gallopavo) | ||
| Common quail (Coturnix coturnix) | ||
| Anseriformes | Ducks and geese | |
| Struthioniformes | Ostriches | |
| Columbiformes | Pigeons |
Poultry may be purchased from any commercial supplier. Poultry breeding companies in the UK will supply fertilised eggs or day-old chicks. Poultry flocks may have high health status or be of conventional status with unknown pathogen load. Researchers should always establish the health and vaccinal status of the supply flock.
By law, all poultry premises with more than 50 birds are required to register with Department for Environment, Food and Rural Affairs (DEFRA). Registration can be carried out on-line at http://poultry.defra.gov.uk.
Biology
External features
There is a keratinised beak, without lips or teeth. The legs are covered in scales, and the remainder of the skin is covered in feathers, of which there are five types, each modified for a different purpose, such as flight, insulation, camouflage and sexual attraction. There are no sweat glands, but an oil gland (preen gland) is located on the back at the base of the tail. Female chickens also have a brood patch; an area of featherless skin on the underside of the abdomen, which is well supplied with blood vessels to transfer heat to the incubating eggs.
Skeleton
The skeleton of birds must be light enough to fly and yet strong enough to support the large pectoral muscles required for flight. To achieve lightness, the medullary cavities of some of the long bones are filled with extensions of air sacs. However, this leaves the cortices of the bones considerably thinner than those of mammals, which make the bones quite brittle and susceptible to fracture. The forelimbs are modified as wings, with fusion of many of the bones to provide additional strength. The sternum of birds is massive, to allow for the attachment of the muscles of flight.
Cardiovascular system
The heart is four-chambered, and larger in proportion to body weight than that of mammals. All avian red blood cells possess a nucleus.
Respiratory system
Birds do not possess a diaphragm, and the lungs are non-lobar and do not expand as in mammals. In chickens, the lungs connect with nine air sacs, some of which extend into the long bones. Birds breathe by expansion and contraction of the chest wall, acting as bellows. Air passes through the lungs into the air sacs during inspiration, then through the lungs again on expiration. Gas exchange in birds is highly efficient, taking place on both inspiration and expiration.
Digestive system
In birds there is an oropharynx, with no soft palate. In many birds, including poultry, the oesophagus has a muscular dilatation half way along its length called the crop. This acts as a food store, and softens and regulates its flow. The stomach is in two parts, the secretory proventriculus, and the muscular ventriculus or gizzard, which grinds the food. In chickens kept outdoors the gizzard will contain grit to assist in this process. There is a short colon with two large caecae.
Renal system
The products of renal excretion are thick and pasty, high in uric acid, but with low water content. The chicken does not have a bladder, so this urate paste is excreted via the ureters, which open directly into the cloaca. The urate paste shows as a white cap on some faecal stools. Kidney failure will result in more dilute urate paste, which can be mistaken for diarrhoea.
Reproductive system
Female birds have only one functioning ovary and oviduct (the left), leading directly to the cloaca. The male has two intra-abdominal testes located by the kidneys. The ducta deferentia open into two papillae on the wall of the cloaca.
Domestic Chicken
The domestic chicken, Gallus gallus domesticus, is a subspecies of the red jungle fowl. It is by far the most numerous species of bird on Earth, with an estimated 50 billion worldwide. In the UK approximately 800 million chickens are killed and 100 000 tonnes of eggs are processed every year for human consumption.
Chickens possess a fleshy protuberance on the top of the head (the comb), and two fleshy protuberances under the chin (the wattles). These can vary in size and shape between breeds, but are usually larger on the male than the female. They act as thermal regulators, and the comb is also a sexual display organ in males.
Behaviour
Chickens are ground-living birds, unable to fly for more than short distances. They are highly social and form stable groups. The behaviours that are most important to them are nesting, perching and using substrate for scratching, pecking and dust-bathing. Given the opportunity, chickens spend a great deal of time performing foraging behaviour (pecking and scratching the ground), and foraging opportunities should be provided for chickens housed in the laboratory. Feather pecking, which can be seen in cage kept birds, is believed to be misdirected foraging behaviour, rather than aggression.
Housing
Chickens should always be kept on solid floors with a suitable substrate if possible. If cages with grid mesh floors must be used, then birds should be provided with a solid resting area occupying at least a third of the cage floor. Perches should always be available and nest boxes provided for laying birds over 16 weeks of age. Note that some hybrid strains of broiler chicken can grow very quickly, so good forward planning is required to ensure that adequate space is available for the duration of the experimental period.
Cleaning regimes will vary according to the type of accommodation. If kept in deep litter systems this is usually wood shavings or straw, which should be dry and friable. If drinker management is poor, or the ventilation is inadequate, the litter can become wet or consolidated. Bird droppings will then remain on top of the litter, which will in turn lead to soiling of the birds, scabby hocks and breast blisters, and will also predispose to respiratory infections.
Dust and dander from domestic poultry may present a risk to people with allergies or respiratory infections. Appropriate cleaning regimes, ventilation and protective clothing are therefore required.
Feeding
Chickens bred for prolific egg laying tend to be small, whereas those used as broilers or broiler breeders (meat-type) have rapid growth rates and a large body size and are less efficient egg layers. Nutritional requirements differ for these two kinds of chickens. Note that some commercial feeds contain a coccidiostat to prevent coccidiosis, and some coccidiostats for chickens can be toxic to turkeys.
For growth, laying chickens need a diet containing 18% protein initially, reducing to 16–17% as egg laying approaches (approximately 20 weeks). Diets are usually based on cereals, with a metabolisable energy content of approximately 2850 kcal (11 930 kJ)/kg of diet
Broiler chickens need up to 23% protein initially, reducing to 18% by weeks 6–8. The diet should have a metabolisable energy content of approximately 3200 kcal (13 400 kJ)/kg of diet2.
Poultry are sensitive to abrupt diet changes, so changes in feed must be made gradually by mixing the feed in decreasing proportions of ‘old’ feed over a few days. In some birds the feed intake may be restricted to control growth rate, as too rapid growth in broilers can cause lameness, or circulatory problems. It is important to feed the correct rations, and with restricted diets particularly there must be adequate space for all the birds to feed at the same time.
Newly hatched chicks need to be encouraged to feed by placing feed on chick paper, or on flat trays, where they can walk and feed easily. Chicks can survive for the first few days on the remnants of the yolk sac, but if they are not feeding by day 4 they will die of starvation (known colloquially as ‘starve out’).
Feeders must be cleaned out regularly, or food will go mouldy, risking the production of mycotoxins.
Water
This is usually provided by automatic drinkers. One nipple or cup drinker should be provided for every four birds, with a minimum of two in every enclosure. They must be cleaned regularly to prevent the build-up of pathogens. As the birds gain weight the drinkers must be raised such that the water is available at head height. Leaking and overflowing drinkers must be avoided.
Environment
The light intensity and the total length of photoperiod controls egg laying. Under natural lighting chickens often lay throughout the winter in their first season, but will go out of lay in the autumn in subsequent years, starting again as the days get longer. Increasing light intensity and photoperiod can prolong the egg-laying period. Feather pecking can be a problem in group-housed chickens, and subdued lighting has been used as a control measure to reduce the incidence of this. However, this should be discouraged, and a lighting level of at least 20 lux is recommended3. Feather pecking is better controlled by providing adequate environmental enrichment. Any increased activity resulting from the use of higher-intensity lighting can be offset by using red filters, which the birds see as dark. Wherever possible there should also be a dawn and dusk period.
Chickens should be kept at temperatures between 15 and 24°C, depending on age3. Additional heat lamps may need to be provided for young birds, in which case the birds must always have sufficient space to regulate their own environmental temperature by moving away from the lamp.
It is very important to provide efficient ventilation without draughts. Inadequate ventilation results in a build-up of airborne dust, microorganisms, water vapour and ammonia. The specialised respiratory system of birds makes them particularly vulnerable to inhalation of particulate matter and the development of respiratory infections. The presence of a significant odour on entering poultry rooms is a good indication that the air-handling system is not functioning correctly.
Birds are more tolerant than mammals to changes in relative humidity and a range of 40–80% is generally acceptable. However, extreme variation in humidity can affect the rate of heat loss in birds, which will influence feed intake and activity.
Birds are susceptible to stress and sudden or prolonged noise can have a detrimental effect on their welfare and production. The general background level of noise in a room should be less than 50 dB, below a noise-rating curve of 45, and free from distinct tonal content.
Breeding
Female chickens begin egg laying from about 18 weeks of age, and males begin to produce semen from as early as 8 weeks. Variation of the photoperiod and temperature are used to stimulate egg production in both laying and breeding birds. Most chickens bred for commercial egg production will lay an egg nearly every day from about 18 weeks of age, depending on satisfactory growth and light levels.
Under natural conditions hens lay until a certain clutch size is reached (usually 12), and then stop laying to incubate all the eggs. She will sit on the nest, and defend it if disturbed, and may not leave the nest to eat, drink or dust-bathe. The hen maintains the nest at a constant temperature and humidity, and turns the eggs regularly.
After mating, semen can take several days to reach the infundibulum, where fertilisation takes place. The fertilised oocyte enters the oviduct, where the layers of albumen are added first, followed by the two shell membranes. The main part of the shell, composed principally of calcium carbonate, is added in the shell gland at the end of the oviduct, over a period of about 20 h. The whole process from fertilisation to laying the egg takes 24 h.
The chicken embryo then requires 21 days incubation before it is sufficiently developed to hatch (28 days in turkeys). However, fertilised eggs will not begin development until the temperature rises above 21°C, and if they are stored at 12–15°C and 75% humidity they may be kept fertile for up to 14 days. The temperature can then be raised to 37.5°C by putting them in an incubator, which is known as ‘setting’ the eggs. Best results are obtained if eggs are incubated within 4–7 days of laying, and fertility drops sharply if they are stored beyond 14 days. During incubation the eggs must be kept warm and occasionally rotated. Incubators are closely controlled for temperature, humidity and ventilation, and the egg trays also gently move periodically, to mimic the action of the hen. Temperature regulation is critical, and variation from the optimum of 37.5°C reduces hatch rates. Relative humidity is also important, because this controls evaporation. Evaporation causes contraction of the fluids in the egg, resulting in the formation of an air sac between the two shell membranes. The size of the air sac, and thus the degree of evaporation, can be assessed by candling. This involves shining a bright light through the egg shell, and can be used to assess the viability of the developing embryo and the network of blood vessels surrounding it.
For best results eggs should be placed with the pointed end down and turned regularly (at least three times per day) until 1–3 days before hatching. If the eggs are not turned the embryo may stick to the shell, resulting in physical defects in the chick. Adequate ventilation provides the embryo with oxygen and prevents build-up of carbon dioxide.
Handling
Domestic chickens are normally docile and do not usually present a threat to handlers. However, they can peck, scratch or hit out with their wings, so caution is required. They are more used to human contact than most species of bird, but can become distressed if they are not handled competently. Rough handling may result in bruising or broken bones, whereas holding birds too tightly may restrict the movement of the chest wall, preventing respiration and causing asphyxia.
Chicks and young birds up to 7 weeks of age should be approached quietly and a hand placed over the bird's back to gently restrain the wings against the body. Once held in this fashion they can be turned over, so that the chick is restrained on its back.
Adult chickens are most easily caught by placing a hand on the back and restraining the wings. Lift the bird by supporting under the body and restrain the bird by holding it against the chest. Once restrained, the hands can then be transferred to take hold of both of the legs, to support the bird's weight (Figure 14.2).
FIGURE 14.1 Handling a chicken. (a) Pick the chicken up with both hands, ensuring the wings are restrained. (b) Hold the chicken against the body, restraining the wings and legs.
Warning: do not catch any bird by the legs, as this will lead to flapping of the wings with possible damage to the bird or the handler.
Techniques
Identification
Poultry are best identified by dyeing the feathers, or by the use of open or closed leg rings. Wing tags and electronic tags can be used, although they are more invasive. When leg or wing tags are used on chicks care must be taken to allow for growth.
Administration of substances
Intravenous
Intravenous injections are often carried out via the alar (wing) vein, found on the underside of the wing, running across the surface of the humeral–radio–ulnar joint, directly beneath the skin. Alternatively, the jugular veins run either side of the neck. Featherless tracks of skin overlie the veins and can help identification of their position.
The medial metatarsal vein is situated on the medial side of the lower leg. Care should be used with this site, as it may cause lameness.
Intramuscular
This should be performed into the pectoral muscles, which are situated on either side of the sternum. Birds have a renal portal circulation, which means that substances injected into the hind quarters of a chicken may be transported by the femoral vein to the kidneys and excreted, before entering the general circulation. For this reason it not advisable to use the leg muscles for injections.
Subcutaneous
Subcutaneous injections should be given under the skin over the keel bone.
Oral
Oral dosing is performed using a needle with a pear-drop end.
Inoculation of chicken eggs
The injection site must first be determined by candling and a small hole drilled through the shell using a glass cutter. A fine needle (13 mm, 27 G) is then passed through this hole to the required site of administration. A needle guard is used to prevent too great a penetration. The hole in the shell is sealed with melted paraffin, and the eggs are returned to the incubator.
Collection of blood
Blood is normally collected from the alar vein, or from the jugular vein if larger quantities are required. Blood removal must be carried out carefully to minimise haematoma formation. The blood may be collected directly into a micro-hematocrit tube.
Cardiac puncture must only be used for removal of blood as a terminal procedure under general anaesthesia and be followed by an approved method of euthanasia. Place the bird on its back and insert a 20–22 G needle from the neck along the ventral floor of the thoracic inlet, avoiding the crop.
Pain and stress recognition
Responses to pain in birds are more subtle than with most other species. They often adopt a hunched posture, and display wing droop. The feathers become ‘ruffled’, which may be exacerbated by lack of grooming, and the bird will separate itself from the cage mates. They may develop an increased respiratory rate and ‘mouth breathe’ when distressed. There may also be changes to the colour of the wattles or comb and evidence of oculo-nasal discharges, and the droppings may become looser.
With severe pain, birds can develop a catatonic response, where they become immobile and totally unresponsive. With chronic pain there will be a loss of appetite and weight, which can best be measured by weighing the bird on a daily basis.
Common diseases and health monitoring
Zoonoses
Domestic poultry suffer from a number of zoonotic diseases. Campylobacter and Salmonella do not usually cause clinical disease in poultry, but may cause disease in humans. Ornithosis (psittacosis), caused by Chlamydophilia psittaci, is a serious, potentially fatal, respiratory disease of humans that can be carried by many types of birds, including domestic poultry. Avian influenza is primarily a disease of birds, but there have been a number of human cases, mostly in south-east Asia, in people who have been closely associated with infected birds.
Clinical diseases of birds
There are many bacterial, viral, parasitic and metabolic diseases of domestic chickens.
Newcastle disease (fowl pest) and avian influenza can both cause rapid, unexplained, high mortality in flocks. These are notifiable and suspicion of these diseases must be reported immediately to DEFRA.
Many of the most serious chicken diseases are caused by respiratory pathogens. These include mycoplasmosis, infectious bronchitis (coronavirus) and infectious laryngotracheitis (herpesvirus). There are vaccines available for these diseases. Mareks disease and avian leucosis are also important viral infections in chickens.
Coccidiosis is extremely common in chickens. Infection with any one of nine species of this protozoan can result in weight loss, diarrhoea and death. Other parasites that infect poultry include nematode worms, such as intestinal, caecal, gizzard and tracheal worms, and ectoparasites, such as red mites and scaly leg mites.
There are a number of vaccines available for use in chickens and turkeys and these are widely used in commercial poultry farms. It is wise to check with the supplier to ascertain which diseases purchased chicks may have been vaccinated against.
More information on poultry diseases can be found at www.thepoultrysite.com.
Biological data and useful reference data
General husbandry data for chickens are given in Table 14.1. Values for feed intake and water consumption will vary with the type of bird kept and the accommodation of the birds.
Table 14.1 Biological data: chickens.
| Biological data | |
| Adult weight (kg) | 1.5–4 |
| Diploid number* | 78 |
| Food intake (g/day) | 125–250 |
| Water intake (ml/day) | 200–300 (should provide ad libitum) |
| Natural lifespan (years) | 5–8 (can live up to 30 years) |
| Rectal temperature (°C) | 41.5 (41–43) |
| Heart rate/min | 180–250 |
| Blood pressure, systole (mmHg) | 71–95 |
| Blood volume (ml/kg) | 60–90 |
| Respiratory rate/min | 15–25 |
| Breeding data | |
| Sexual maturity (weeks) | 18–24 female, from 8 weeks in male |
| Age to breed (weeks) | 20–23 |
| Incubation (days) | 20–22 |
| Clutch size | 1–14, if eggs removed birds lay daily for up to 1 year |
| Weight at hatching (g) | 50–70 g |
| Haematological data | |
| Red blood cells (×106/mm3) | 2.5–3.5 |
| PCV (%) | 22–35 |
| Hb (g/dl) | 7–13 |
| White blood cells (×103/mm3) | 12–30 |
| Hb, haemoglobin; PCV, packed cell volume. *Birds have a number of macrochromosomes that are of normal size, and also microchromosomes which are of reduced size and are difficult to count. This figure includes 60 microchromosomes. |
|
Anaesthesia of chickens
All avian species present special difficulties with regard to general anaesthesia. Birds have higher metabolic rates and higher resting temperatures than mammals of equivalent size. The higher temperatures lead to greater heat loss during anaesthesia. The high ratio of surface area to body weight also increases the heat loss, so it is particularly important to minimise this during anaesthesia by maintaining a high environmental temperature and providing insulation. Avoid removing large numbers of feathers and chilling the body by application of fluids, such as surgical spirit.
Fasting pre-anaesthesia should generally be avoided as the higher metabolic rate of birds can induce hypoglycaemia. This is particularly important for birds under 1 kg body weight.
Induction of anaesthesia may be by injection or inhalation. Chicks may be induced by placing them in an induction chamber. Once anaesthetised they may then be maintained via a face mask or an endotracheal tube.
The two-stage respiratory cycle of birds and the presence of air sacs can allow a build-up of anaesthetic gases in the dependent areas of the respiratory system, which may lead to anaesthetic overload. Care must be taken not to obstruct respiration, as even short periods of apnoea can be fatal. Avoid taping the wings and legs in full extension, as this can inhibit both respiratory movements and venous return.
Birds should recover in a quiet dark environment at a temperature maintained at 40°C. All cage furniture must be removed to avoid injury. It is also a good idea to temporarily fix the wings by taping them to the body with micropore tape, to prevent damage from flapping during the recovery period.
Warm isotonic saline may be given by subcutaneous or intravenous administration, at 5 ml/kg. Birds should be encouraged to eat as rapidly as possible after recovery. Unfortunately there is little known about the effectiveness of analgesia in birds. Dose rates for anaesthesia in chickens are given in Table 9.3d.
Ruminants
Ruminants are kept worldwide for their meat, milk, skins and wool (sheep), or hair (goats). The ruminant most commonly used for scientific studies in the UK is the sheep, but small numbers of cattle, goats and deer are also used. Figure 14.3 shows a simple classification for ruminant species. Note that species in the family Camelidae, in the suborder Tylopoda, are not true ruminants. This includes camels and the South American llamas, alpacas, guanacos and vicunas.
Figure 14.3a Classification of ruminants.
Ruminants are generally acquired from commercial suppliers, which are normally commercial farms. It is not recommended that ruminants are purchased through markets or dealers, as these animals will usually have been derived from a number of different farms, with no medical or husbandry history.
Most commercially farmed ruminants are reared under conventional conditions and the husbandry and health of such animals can be extremely variable. Whenever practicable, veterinary inspection and health screening of the animals should be undertaken on the farm of origin before transport to the research facility. It is advisable to isolate all animals on arrival for a period of 4 weeks, during which time clinical assessment, tests and treatments may be carried out. The following general rules should be observed whenever possible:
- purchase from as few sources as possible,
- purchase as infrequently as possible,
- ensure the source herd is free of pathogens that are significant for the species and the research,
- isolate incoming stock for as long as possible (4 weeks, if possible),
- during isolation, medicate for endemic pathogens, such as ecto- and endoparasites.
To maintain the health status of an established farm-animal facility it is essential to impose a continuing high level of biosecurity. Personnel and animals, and feed, bedding and other equipment, are potential sources of disease. The following procedures are advised.
- Visitors should be kept to the absolute minimum and should not enter within 48 h of same-species contact. As a minimum, a full change of protective clothing should be provided before entering the unit.
- Loading and unloading procedures must be strict. All livestock vehicles present a potential disease risk.
- The proximity of other animal units and major roads should be considered when siting a new unit. Some airborne pathogens can be carried for several kilometres.
Sheep
The sheep (Ovis aries) was derived from the mouflon (Ovis orientalis) by domestication over 10 000 years ago. There are more than 200 sheep breeds worldwide, with over 60 of these found in the UK. They vary in size from small native breeds such as the Soay or Shetland (adult female 25–30 kg), to the much larger down breeds, such as the Suffolk and Oxford (adult female 85–90 kg). Breeds also differ widely in temperament and fleece characteristics, and may be either horned or naturally polled. There are approximately 14 million sheep in the UK, the majority of which are bred for meat (lamb) production. Most of the breeding females are actually F1 hybrids of two pure breeds. These ewes are then crossed with a terminal sire to produce an F2 lamb for slaughter. Unlike pigs or poultry there are no UK commercial sheep-breeding companies.
In research, sheep are commonly used for antibody production, since they are easily handled and large quantities of serum (up to 500 ml) can be regularly harvested. They are also used for studies on fetal development, reproduction, endocrinology, respiratory function and orthopaedics, as well as a number of sheep diseases of economic and public health importance.
Behaviour
Sheep are very social animals that are normally docile and tractable. At pasture they spend a large part of the day grazing over wide areas, but they are timid and have very strong flocking instincts. If disturbed they rapidly flock together, which makes them relatively easy to drive. However, their well-developed flight reflex can easily turn into a headlong rush, in which injuries can occur. They will more readily move uphill, and away from dark towards light, and this should be borne in mind when designing handling facilities. Sheep become distressed if separated from others, and should never be housed singly, unless justified for experimental reasons, in which case they must always be within sight and sound of conspecifics. Entire males can be aggressive to humans.
Housing
Sheep are able to adapt to a number of different types of housing. They may be kept outdoors at pasture, or in covered or semi-covered yards, or in totally enclosed accommodation, which may or may not be environmentally controlled.
Their thick lanolin-impregnated fleeces make them well adapted to severe weather conditions and they can remain outdoors throughout the year in the UK, providing shelter from wind and driving rain is available. Fencing needs to be close-meshed and robust, approximately 1 m high, and free of sharp projections that may cause injury. Sheep do not usually jump over fences, but will test their strength by rubbing and pushing against them until they break. Outdoor housing has many environmental advantages for sheep, but they will be exposed to both internal and external parasites, and parasite-control programmes will be need to be drawn up. Young lambs may also be liable to predator attack (from dogs or foxes).
If sheep are kept indoors it is advised that they are kept in groups of no more than 30, matched by age and size to prevent bullying at feeding. Horned sheep should not be housed in the same enclosure as polled sheep.
The walls and doors of the enclosure should be non-porous and easy to clean. The lying area must have a solid floor, made of concrete or rammed chalk, which gives better drainage. Bedding should preferably be deep straw to provide insulation and comfort, although wood shavings or sawdust may be alternatives. Fresh, clean, dry bedding should be added on a regular basis, until the height of the bed requires its removal. The pen should then be washed down and allowed to dry before re-bedding.
Environmental enrichment can be difficult with sheep. Toys, such as balls or chains, do not seem to be of much interest to sheep. The provision of conspecifics, roughage and space to lie down to ruminate is probably the most important enrichment for housed sheep. Un-chopped root vegetables, such as sugar beet, are well liked and give them something to gnaw at. They may be provided as a treat on a daily basis, although in the long term there is a risk of damage to the incisor teeth.
Breeding ewes are usually housed in individual pens with their lambs for a few days at lambing time. This ensures that the lambs receive colostrum and develop the maternal bond. After 24–48 h ewes and lambs can be mixed with others in small groups.
Feeding
Sheep are obligate herbivores and their digestive tracts have adapted to a diet of vegetable matter. They have no upper incisor teeth, but in their place possess a hard, ridged fibrous ‘dental pad’, against which the lower incisors bite. They have no canine teeth, leaving a gap, the diastema, between the lower incisors and the molar arcades. The molars are continuously growing and adapted for grinding fibrous food. The jaw is articulated to allow movement from side to side for efficient chewing.
The non-glandular fore-stomach consists of three large chambers: the reticulum, the rumen and the omasum. The rumen and reticulum contain bacteria that digest cellulose, releasing fatty acids, and produce vitamins. Food from the rumen is regurgitated several times for extra chewing, in a process known as rumination. A side effect of the breakdown of cellulose is the production of large quantities of methane gas. This is removed from the rumen by frequent belching (eructation), which may occur as often as once every minute. If ruminants cannot release the gas produced, the methane will accumulate to distend the rumen, causing the condition commonly known as ‘tympany’ or ‘bloat’. In severe cases the pressure of the distended rumen will cause circulatory disturbance and, unless relieved, death.
Food eventually passes from the rumen, through the omasum, which absorbs much of the fluid, to enter the abomasum, which is analogous to the glandular stomach of other mammals. In young lambs the rumen is undeveloped and milk passes via a muscular groove (the oesophageal groove) to enter the abomasum directly. The rumen gradually develops in response to the ingestion of roughage, and is fully functional by about 8 weeks of age. Sheep produce copious quantities of saliva, but do not vomit. However, drooling and spillage of regurgitated rumen contents may be seen.
Sheep are grazing animals and will nibble grass and vegetation at ground level. Under most circumstances they will obtain sufficient nutrients for growth and maintenance from grass alone. The optimum sward height for sheep is 2.5 cm, and they can have difficulty utilising very long grass. If the grass quality or availability declines sheep should be fed a long-fibre conserved forage, usually hay but alternatively silage or even straw. In some circumstances, such as pregnancy and lactation, the ewe's diet may require supplementation with higher energy ‘concentrate’ foods. Concentrates are normally based on cereals, with additional protein, vitamins and minerals. Approximately 125 g/head per day of a commercial sheep food should be fed daily from day 100 of pregnancy, gradually increasing to as much as 1 kg/head per day at parturition. Sheep fed on straw as their sole source of roughage overwinter, will require additional concentrate feeding.
Whenever sheep are kept indoors roughage should be permanently available in hayracks. If concentrate rations are also fed there must be sufficient room at the feed trough for all animals in the pen to feed at the same time. Where horned animals are kept additional space allowance must be made at the feed troughs to avoid injuries.
Mineral deficiencies may occur if the pasture or conserved foods are deficient in copper, cobalt or selenium. Supplementary minerals may be advised in these circumstances, but great care is required in their formulation, as sheep are peculiarly susceptible to copper toxicity. Concentrate rations or minerals intended for cattle or pigs contain added copper and should never be given to sheep, as they can induce copper toxicity.
Poor dentition can be a problem in older sheep. The incisor teeth are frequently lost. However, the majority of sheep can maintain satisfactory body condition without incisor teeth. Of more importance are the molar teeth, which are essential for masticating food. Loose or infected molar teeth are a common cause of weight loss in older sheep.
Growing sheep are particularly prone to urinary calculi when fed high levels of concentrate. In male lambs (entire or castrated) the urethra is narrow, and calculi may cause urethral blockage, with urine retention and fatal consequences. To prevent this it is essential that the magnesium and phosphorus content of concentrate rations be restricted. Salt licks should always be provided to encourage drinking and urinary throughput, and urinary acidifiers may also be helpful.
Water
Sheep must be provided with clean water ad libitum at all times. They prefer to drink from flowing water, although this may be difficult to achieve in practice. Static water tanks are acceptable, but care is required because sheep can become cast in them and drown. Bowl drinkers are satisfactory in indoor pens, but nipple drinkers are not suitable for sheep.
Environment
Sheep will tolerate a very wide range of temperatures. The thermoregulatory neutral zone for sheep is 10–30°C, but the extremes of this range depend on whether they have a full fleece or not. Unshorn sheep in summer can suffer from heat stress, exhibiting panting and mouth breathing at temperatures over 20°C. This is exacerbated if they are kept indoors, and in these circumstances shearing should be undertaken in April or May, well in advance of any hot weather. Once shorn, sheep are more susceptible to cold and should not be exposed to temperatures of less than 10°C. If shearing is undertaken very early in the year they must be housed for at least 2 months before they are turned outside, to allow some fleece re-growth. Sheep permanently housed in environmentally controlled conditions will generally benefit from shearing twice a year, and should be kept at between 10 and 24°C. Adequate ventilation is essential to reduce the risk of respiratory disease. Extractor fans should remove 3 m3 air/kg of body weight per hour to control ammonia levels and humidity levels should be kept between 45 and 65%.
Breeding
Sheep are seasonally polyoestrous, returning into oestrous every 16–17 days over the winter period (September–February). The onset of the breeding season is controlled by diminishing day length, but varies significantly between breeds. Normally the hill breeds start later (October–November) than the lowland breeds (August–September). Dorset sheep are unusual in having a very long breeding season, extending from about June to March. This means that they may be mated every 8 months, giving birth to three litters in 2 years. Dorset breeds and their crosses, particularly the prolific Finn-Dorset, are popular research animals.
Under farm conditions ewes are normally mated in the autumn, to give birth the following spring. They run with the rams (tups) for a period of about 6 weeks. Ultrasound scanning at 50–90 days of gestation is widely practised to determine pregnancy and count fetal numbers. Ewes carrying multiple fetuses can then be grouped separately for differential feeding.
Gestation lasts approximately 147 days (range 142–150 days), although there are slight breed differences. Ewes carrying multiples normally have shorter gestation times than those carrying single lambs, but as a rough guide, in the northern hemisphere, ewes mated on Guy Fawkes day (5 November) will lamb the following All Fools Day (1 April). Ewes may be mated as lambs (ewe-lambs) in their first autumn, at about 6 months of age, provided their body weight is at least 70% of the adult weight for the breed. Alternatively, they may be left until the second autumn, when they are 18 months of age. Weaning normally takes place at 12–16 weeks, although there are management systems where weaning may be as early as 6 weeks, provided suitable concentrate rations are provided.
In most sheep breeds the breeding season can be advanced by a number of methods. These include the use of progesterone-impregnated intra-vaginal sponges, melatonin implants or the use of vasectomised males. By advancing the breeding season in the UK to July or August lambs can be produced in December/January. Artificial insemination (AI) is possible in sheep using either fresh or frozen semen, and embryo transfer may also be carried out by laparoscopy under general or local anaesthesia.
Handling
Sheep are particularly easily startled and patience and gentle handling are required for success. They are inclined to follow one another, and will generally move away from humans, dogs or buildings towards open countryside. Where larger numbers are involved a proper sheep-handling system should be employed.
Where sheep are held indoors carefully designed housing, consisting of holding pens leading through narrow walkways and races to smaller pens, will allow individuals to be caught with minimal stress. Where such facilities do not exist the best method of restraint is to gradually pen the sheep into a corner using a number of hurdles. A trained handler can then restrain the individual sheep, by holding one arm under the neck and the other around the rump (see Figure 14.4). Sheep should never be caught by the wool, as grasping the fleece is painful and may result in handfuls of wool being torn out. It is also not advised that sheep be caught by their horns. It is an offence under welfare legislation to lift a sheep by its horns.
FIGURE 14.4 Restraining a sheep.
To turn a sheep onto its rump (casting), the handler stands on the left side of the sheep, grasps the muzzle with the left hand, and pushes the head round to the right to face the tail. This can be facilitated by placing the thumb in the diastema behind the incisor teeth. With the right hand, press down on the rump and the hind legs will collapse. The sheep can then be rolled over and sat onto its rump (see Figure 14.5). Alternatively, with smaller sheep, the handler may be able to reach over and grasp the fold of skin low down on the right flank. Using this fold the sheep can be lifted up so that it comes to rest sitting on its rump.
FIGURE 14.5 Casting a sheep.
Pain and stress recognition
Sheep in pain appear dull and depressed with little interest in their surroundings. They may become anorexic, have drooping ears and be reluctant to rise. However, sheep have a great ability to mask the signs of pain, and in the early stages these may only be apparent to an experienced stockperson. In the later stages separation from the group is a good indication that a sheep is sick. Nasal discharge is a common sign of respiratory infection, and grunting or teeth grinding usually indicate abdominal pain. Lameness is a common problem with sheep and should never be ignored. Animals are not lame unless they have pain in the limb.
Common diseases and health monitoring
Sheep are susceptible to a number of diseases, many of which are zoonoses. Very few commercial flocks have a well-defined health status, so it is safest to assume that all sheep are carrying a wide variety of sheep diseases and to screen any that are purchased for research purposes thoroughly. The rules for isolation and biosecurity outlined in the introduction to this section should always be followed.
Zoonoses
Of particular concern are the numerous zoonotic agents that may cause abortion in ewes (Chlamydophilia, Toxoplasma, Campylobacter, Listeria, Coxiella and Salmonella). For this reason it is advised that pregnant women do not handle ewes or lambs at lambing time. Contagious pustular dermatitis virus (Orf) is a common viral disease of sheep, causing facial lesions in lambs and a painful skin condition in humans. The protozoan parasite Cryptosporidium parvum may cause enteritis in lambs and humans.
Clinical diseases
Parasitic gastroenteritis (PGE) caused by gastrointestinal nematodes is a common and potentially fatal condition of lambs, and constitutes the major health threat to young, grazing sheep. Control can only be achieved by routine prophylactic anthelmintic treatment. However, increasingly worms are becoming resistant to many of the anthelmintics available. Veterinary advice should be sought on the selection and frequency of treatments. Sheep born and reared indoors are very unlikely to suffer from PGE. However, if grazing sheep are moved indoors they will almost certainly be carrying these parasites, and will need treating with an anthelmintic on housing. Liver fluke is another life-threatening parasite of sheep, associated particularly with grazing pastures prone to flooding.
Lice and psoroptic mange (sheep scab) cause irritation and wool loss in sheep. Treatment may be by contact chemicals or injection. Ticks and keds are important vectors of other diseases, particularly in the hill regions. Myiasis (fly strike) is seen in the summer and autumn months in the lowlands. Undetected, fly strike can prove fatal and prompt treatment is required.
Foot rot is a common infectious disease of sheep, caused by the bacterium Dichelobacter nodosus. It spreads rapidly when infected sheep are housed indoors, so prophylactic treatment at housing should be undertaken.
Clostridial diseases are common and nearly always fatal. These include diseases such as tetanus, and enterotoxaemias caused by Clostridium perfringens. Effective clostridial vaccines are commercially available and should always be used. Mannheimia haemolytica and Pasteurella multocida are common commensals found in the throat and nasal passages. Under stress, and particularly in conditions of poor ventilation and overcrowding, they can produce acute or chronic respiratory and systemic disease. Vaccines are available and should be routinely used in housed sheep. Other important bacterial conditions include Corynebacterium pseudotuberculosis (caseous lymphadenitis) and Mycobacterium avium pseudotuberculosis (Johne's disease).
Border disease virus (BDV) can produce infertility and fetal abnormalities. Maedi–Visna (M–V) and sheep pulmonary adenomatosis (SPA) are viral causes of chronic respiratory disease but may combine with Ma. haemolytica to produce acute disease.
Scrapie is a notifiable disease, and suspicion must be reported to DEFRA. It is slow-onset transmissible spongiform encephalopathy (TSE) of unknown aetiology, producing neurological changes in adult sheep. Resistance to scrapie is genetically controlled. The incidence of scrapie is now very low in the UK.
Anaesthesia and surgery
There are a number of difficulties to be addressed with general anaesthesia in sheep and these, together with their placid and stoical nature, have led to the widespread use of local anaesthetic techniques. The considerations below relate to adult sheep only. Lambs below 8 weeks of age (before the development of the rumen) can be treated as if possessing a single stomach.
Sheep are usually starved for up to 18 h and water withheld overnight before general anaesthesia to reduce the volume of the rumen contents and also reduce the amount of gas produced, particularly if the sheep has previously been at grass.
Sheep produce large quantities of saliva, which may pool in the pharynx during anaesthesia. Regurgitation of rumen contents is also possible. It is advisable to position the sheep with the head lowered and the nose pointing downwards, over the end of the operating table, to allow for drainage of these fluids by gravity. The use of drying agents such as atropine is generally contraindicated in ruminants, as it renders salivary and bronchial secretions more viscous and harder to clear. To prevent accidental inhalation of saliva or ruminal contents once the swallowing reflex has been lost it is also strongly advised that a cuffed endotracheal tube is inserted as soon as anaesthesia is induced. A laryngoscope may be needed for this.
Microbial activity in the rumen continues during anaesthesia, and can lead to a build-up of gases in the rumen, which becomes distended (tympany), interfering with surgical access to the abdomen, and putting pressure on the diaphragm, embarrassing respiration. This may be relieved by the use of a stomach tube. This results in the passage of large quantities of rumenal fluid, which should be collected into a bucket to avoid contamination of the operating theatre floor. Alternatively, a temporary rumen fistula can be created for the duration of the procedure.
If sheep are held on their back for long periods the weight of the rumen compresses the posterior vena cava, compromising venous return to the heart and leading to circulatory collapse. If possible sheep should be positioned with the hind quarters slightly lower, so that the weight of the abdominal contents does not rest on the diaphragm.
Table 9.3e gives suggested doses for anaesthetic and analgesic doses in ruminants. No analgesics are licensed for use in sheep in the UK, so those for other species should be used under veterinary direction.
The rumen occupies the whole of the left side of the abdomen. Abdominal surgery may take place through a mid-line ventral incision, but this requires the sheep to be in dorsal recumbence for a long period and, post-operatively, the weight of the rumen puts great tension on the suture line. For these reasons abdominal surgery is often conducted through an incision made in the left flank. Although this is directly over the rumen, this can be pushed aside to reveal the area of interest (uterus, liver, etc.). If incisions are made in the right flank, the pressure of the rumen can force intestines out of the wound, making it very difficult to operate.
Useful data
Table 14.2 gives useful data for ruminants.
Table 14.2 Useful data: ruminants.
Goats
The ancestor of the modern domestic goat (Capra hircus) is the Bezoar, found in the Middle East and Asia Minor. Selection for milk, meat or skins has led to the development of several breeds, of which the British Saanen, Toggenburg and Anglo-Nubian are the commonest in the UK. Some breeds, such as the Angora and Cashmere, have been developed specifically for fibre production (mohair and cashmere). Varieties of dwarf (pygmy) goats exist that weigh as little as 20 kg. Goats normally possess horns and may also have beards and wattles. The tail is naturally short and stands erect when the animal is alert. They have strong-smelling scent glands around the horns in both sexes and also under the tail in the male.
Behaviour
Goats are inquisitive animals and tend to be more independent than sheep. They normally live in groups, but will cope well if they have other species, such as humans or sheep, for companions. If disturbed they will scatter, relying on their agility over difficult terrain to escape. This makes them impossible to drive, unlike sheep. However, they can be led and will usually follow a handler, especially if they have food. They frequently stand on their hind feet to explore, and can easily reach to a height of 2 m, so this should be considered when suspending items near or above goat pens. Their curiosity causes them to lick or chew at any unusual materials, which can lead to the ingestion of foreign objects and may be the cause of accidental poisoning or even electrocution from suspended electric cables.
Goats form a strong social hierarchy and the introduction of new members to a group may result in fighting. This can lead to injuries because many breeds are horned. Males can be aggressive during the breeding season.
Housing
Goats are less well protected from extremes of cold than sheep and should always be provided with a roofed shelter3. They dislike rain and need a dry, draught-free bed. An open fronted building will usually be sufficient, provided it backs into the prevailing wind. Goats are particularly agile and can leap over barriers several feet high; so all fences should be at least 2 m.
Goats are natural climbers and the provision of a raised area in a pen, such a large straw bale, provides good environmental enrichment. However, they may also use such raised areas to jump out of the pen, so be careful not to site this too close to a fence. Owing to their natural inquisitiveness, goats will investigate objects, such as toys or chains, particularly if these are suspended above head height. The provision of roughage suspended above head height, to allow natural browsing behavior, is also recommended. Goats readily become accustomed to contact with humans, and this should be encouraged during routine husbandry procedures and at other times.
Feeding
Goats are primarily browsing, rather than grazing, animals and will strip vegetation off trees to a considerable height. However, in the absence of trees, goats will graze and can be maintained on grass in paddocks. As with other ruminants, conserved forage, such as hay or silage, must be fed during the winter months.
Lactating goats can produce as much milk per kilogram body weight as dairy cows and will normally require supplementary concentrate feeds. They are less sensitive to the toxic effects of copper in the diet than sheep.
Goats are fastidious eaters, and will refuse food that has been soiled by faeces or urine. Feeding troughs must be clean and hayracks should be suspended well above the floor. This not only prevents soiling of the hay but also allows the goats to perform their natural browsing behaviour.
Water
Goats are fussy drinkers and must be provided with clean water ad libitum at all times. Water bowls must be cleaned out regularly. Lactating goats may drink 10 litres or more of water daily.
Environment
Goats are more heat-tolerant than sheep, but less able to stand extremes of cold. When housed indoors they should be kept at temperatures between 10 and 24°C and at relative humidities of 45–65%.
Breeding
Like sheep, goats are seasonal breeders, commencing their oestrous cycles in the late summer/autumn and ending in mid-winter. Oestrus occurs approximately every 21 days throughout this period. Gestation length is 147–155 days and the litter size is normally between one and three. As with sheep it is possible to advance the breeding season with the use of hormones.
Pregnancy can be confirmed by ultrasound scanning at about 50 days of gestation. Some goats can develop pseudopregnancy, even if they have not been mated. They show increased abdominal and udder swelling over a period of months, which normally results in the eventual discharge of copious quantities of uterine fluid at the expected time of parturition. Such animals usually breed normally in future years. Goats are also unusual in that some will come into lactation without any prior pregnancy or parturition.
Puberty is reached at 5–8 months of age. AI and embryo transfer techniques are available. Kids are normally weaned at 5–6 months of age, although if the dam is producing milk for human consumption the kid will be artificially reared from 4 days of age.
Handling
Goats are usually horned, which can be dangerous for the handler. However, they are generally less nervous than sheep and can be caught quite easily with a little patience. They should not be caught or restrained by the horns, but by holding the hands either side of the head, behind the lower jaw. Unlike sheep, goats should not be restrained by casting, and all examinations should be performed in the standing position, as for a cow.
In order to facilitate future handling most goat kids have their horn buds removed at about 4 days of age (disbudding). If this procedure is delayed beyond a week there is a danger of incomplete removal and re-growth. This procedure must be carried out under general anaesthesia by a veterinary surgeon.
Pain and stress recognition
Goats are usually more vocal than sheep, although they too have an ability to mask the signs of pain. Dullness, drooping ears, reluctance to rise, anorexia, teeth grinding and separation from the group are all indicators of pain or distress.
Common diseases and health monitoring
Nearly all of the infectious diseases of sheep are transmissible to goats, as well as the majority of the sheep parasites. The major differences between the species can be summarised as follows.
- There are no licensed vaccines available for goats. However, some sheep vaccines may be used under veterinary direction.
- Goats are more susceptible than sheep to infections with mycobacteria (Johne's disease and tuberculosis, or TB). They should be routinely tested for TB, especially if they have been in contact with cattle.
- The Maedi–Visna virus of sheep produces arthritis, encephalitis, pneumonia and mastitis in goats, where it is known as caprine arthritis and encephalitis virus (CAE). This is more common in the USA than in the UK. Serological tests are available to detect infected animals.
- Goats do not usually suffer from fly strike, because their short-hair coat is kept cleaner than the long wool of sheep.
Anaesthesia and analgesia
The sedative, anaesthetic and analgesic agents recommended for sheep are also suitable for goats at identical dose rates (see Table 9.3e). Like sheep, goats are extremely sensitive to xylazine and this sedative should never be used.
Cattle
The domesticated cattle of the world are nearly all derived from two major species: Bos taurus, which includes all of the European breeds, and Bos indicus, which includes the Asian and African cattle. By selection, a number of different breeds have developed. Some of these are kept primarily for meat production (beef breeds) and some for milk production (dairy breeds).
In the UK, the Holstein–Friesian is the predominant dairy breed, although Jersey and Guernsey breeds remain in the Channel Islands and areas of the West Country. Holstein–Friesians are the largest dairy breed, weighing over 600 kg (bulls over 1000 kg), while Jerseys are the smallest (400 kg).
Beef breeds include the native Aberdeen Angus and Hereford, as well as continental breeds, such as the Charolais, Simmental and Limousin. Dairy cows are frequently mated to bulls of the beef breeds, to produce hybrid calves with greater growth potential and better carcass conformation than the pure Friesian.
Cattle are not widely used in research, because of their large size and expense. However, they are the species of choice for certain zoonotic infections (Escherichia coli 0157 and TB) and are also used for studies on ruminant physiology related to milk production.
Behaviour
Cattle are gregarious animals, and show clear signs of stress if isolated4. Wild cattle aggregate in groups of cows and calves, with bulls in separate groups. Bulls defend specific areas within the larger environment and occasionally interact with cow–calf groups. Affiliative behaviour includes allo-grooming, or social licking, often directed at the neck. Cows form grooming partnerships with specific individuals within a group.
Aggressive interactions occur when unfamiliar individuals are mixed together, but reduce as animals establish a dominance hierarchy. Aggression is more common in intact males than in castrated steers5. Aggressive behaviours include lowering the head and physical contact (head butting or head-to-head pushing). Bulls may also vocalise, or paw and rub the head on the ground.
Cattle show diurnal rhythms when on pasture. During the day they spend more time grazing, and at night more time lying down. Cattle also spend between 8 and 12 h lying down per day, in bouts lasting about 1 h. The diurnal pattern of feeding and lying down is highly synchronised when cattle are kept on pasture. This can be influenced by other factors, such as weather and access to shade. For example, cattle will spend more time standing and less time lying down in warm weather6 and more time standing in shade during the day with more grazing at night to avoid the heat of the day7.
Dairy cows are normally docile and creatures of habit. They rapidly become accustomed to the regular routines involved in twice daily milking and are habituated to close human contact.
Calves are easily handled up to about 12 weeks of age (100 kg), but as they grow their increasing weight can make them potentially dangerous to humans.
Beef breeds are generally less amenable than dairy breeds, because they are handled less regularly. All bulls are unpredictable and cause several human deaths each year. They must always be handled with extreme caution.
Housing
Cattle can survive outdoors in a very wide range of climates. However, it is customary to bring milking cows and most beef breeds inside for the winter months in the UK. During the grazing season (usually April–October in the south of England), cattle can be kept outside in fields enclosed by wire fencing approximately 1.2 m high.
Housed cattle are normally bedded on deep straw, over a base of concrete or rammed chalk. Part of the floor area (up to 20%) may be slatted to facilitate cleaning. Slatted floors are generally less welfare-friendly than solid floors and must be designed carefully. Groups should be matched by age and size and horned breeds should not be mixed with polled breeds to prevent injuries3.
Over winter, cattle may be housed in straw yards, cowsheds, kennels or cubicle systems. Cubicles may be bedded with straw, wood shavings, sand or lined with rubber mats. For ease of feeding dairy cows are normally grouped according to their date of calving and milk yield.
Environmental enrichment for cattle has not been well defined. Group housing, comfortable bedding and provision of roughage ad libitum are probably the most important aspects. The provision of toys and similar does not appear to elicit much interest.
Feeding
Beef breeds normally graze during the summer months and are fed conserved forage (hay, silage or straw) over winter. They receive little in the way of concentrate feeds and their calves are naturally weaned at 6–7 months of age. Dairy cows require additional concentrate rations throughout lactation, and the feeding of these to maximise milk yield has become a science in itself.
Dairy calves are normally removed from the dam at 2–4 days of age and reared on milk replacers. There are many different systems for artificially rearing calves, ranging from twice daily bucket feeding of warm milk, to fully automatic milk dispensers. Hay and concentrate rations should be made available after 2 weeks and weaning normally takes place at 6–7 weeks, at which time the calves should be eating in excess of 1 kg concentrate/head per day.
Indoor-reared cattle typically eat for 4–6 h/day, while on pasture cattle spend more time grazing, 6–10 h/day. In pasture systems there is space for all cows to feed at once. In barns, restricted space at the food trough make it is less likely that all cows will feed at the same time.
Environment
Calves artificially reared in calf houses are prone to enteric and respiratory diseases. They require temperatures above 15°C, a clean, dry bed of straw and good ventilation, without exposure to draughts.
Weaned calves housed indoors remain particularly prone to respiratory infections and good ventilation (either natural or forced) is essential. Temperatures should be above 10°C and humidity 45–70%. Wide fluctuations in temperature and humidity, as may occur in the autumn, can predispose cattle to pneumonia.
Adult cattle are able to withstand considerable variations in temperature and are normally kept at ambient temperature in sheltered buildings.
Breeding
Cattle are polyoestrous throughout the year, although they are generally less fertile during the winter months. The oestrous cycle lasts 21 days, but can be manipulated by the use of various hormones. Pregnancy can be confirmed by manual palpation per rectum, by ultrasound scanning or by a progesterone assay. Gestation length is 280 days (±10 days), although there are breed variations. Cows normally have a single calf, although twins are not uncommon. They will normally return to oestrus within 42 days of calving and are mated at approximately 85 days, to achieve a calving interval close to 365 days.
AI is practised widely in dairy cattle. Commercial AI centres hold stocks of frozen semen from genetically superior sires and supply a daily insemination service to farms. Embryo transfer is also commercially available for cattle, using stored, frozen embryos.
Handling
Cattle are generally docile and easily handled, but their large size makes a good handling system essential. In research establishments cattle may be trained to feed through a neck yoke, so that they can be restrained and haltered at any feeding time. A cattle crush is necessary to carry out examinations and procedures.
Calves less than 70 kg can usually be restrained by two handlers. One should hold the head, putting a hand across the bridge of the nose (taking care not to obstruct the nares), and turning the head towards them, while the other restrains the rear end. For cattle over 100 kg a halter should be used to restrain the head or the animal placed in a neck yoke or crush (see Figure 14.6).
FIGURE 14.6 Restraint of a cow for blood sampling.
Pain and stress recognition
Cattle show the same signs of pain as sheep and goats. They appear dull and depressed with little interest in their surroundings. They may have drooping ears, show a reluctance to rise and show anorexia. In later stages separation from the group and grunting or teeth grinding may be heard.
Common diseases and health monitoring
Zoonoses
Cattle suffer from several important zoonoses that may be fatal in humans.
- Bovine spongiform encephalopathy (BSE) was common in adult cattle from 1985 to 2000, but has now been eradicated from the UK.
- Regular skin testing for Mycobacterium bovis, the causative agent of bovine TB, is mandatory under DEFRA. It is recommended that cattle should be tested for this additionally before introduction to a research establishment. Mycobacterium avium paratuberculosis (avian TB) is seen occasionally in adult cattle over 2 years of age.
- Salmonellosis is a common cause of diarrhoea in neonatal calves, particularly if they have been traded through a market. All purchased calves should be tested on arrival.
- Leptospira hardjo can be carried asymptomatically by cattle and transmitted to humans via splashes of infected urine. A vaccine is available and should be used routinely.
- E. coli is common in calves, and may be asymptomatic. However E. coli 0157 may be fatal to humans.
- Brucella abortus has been eradicated from the UK but remains an important zoonosis in many parts of the world.
- Calves frequently suffer from ‘ringworm’, a fungal skin disease that is commonly transmitted from cattle to handlers.
Clinical diseases of cattle
Parasitic infections are less important in cattle than sheep, although young calves may be badly affected. Liver fluke, seen when ruminants graze pastures liable to flood, can cause severe disease in both sheep and cattle of all ages. Lungworm, due to Dictyocaulus viviparus, can cause pneumonia in all ages of cattle, but there is a vaccine available. Coccidiosis may be problematic in young calves, especially when reared indoors.
Three respiratory viruses are common in cattle: bovine respiratory syncytial virus (BRSV), parainfluenza 3 virus (PI3), and herpesvirus 1 (infectious bovine rhinotracheitis, IBR). They often produce disease in association with bacterial agents, such as Ma. haemolytica, M. bovis and Haemophilus somnus.
Rotavirus and coronavirus infections are also common causes of diarrhoea in neonatal calves. Bovine virus diarrhoea (BVD) is very common, but clinical signs are usually mild with complete recovery. However, if infected during pregnancy the fetus may be aborted, or mutated, or if the calf is born alive it may be persistently infected with the virus. Persistently infected calves are immunosuppressed and are unsuitable for use in research. They also act as a source of BVD infection for other cattle and will cause severe fertility problems in a herd. All purchased cattle should be tested for their BVD status by blood sample before arrival.
Cattle may suffer from lice infestations, but do not generally suffer from fly strike.
Anaesthesia
By virtue of their placid nature and large size cattle are particularly suited to regional nerve blocks, such as epidural and paravertebral. If general anaesthesia is given the precautions given above for sheep and goats apply. Drug doses are listed in Table 9.3e.
In adult cows the endotracheal tube may be introduced into the trachea by inserting a hand into the back of the mouth and guiding it into the larynx. A gag should always be in position between the molar arcades to prevent accidental closure of the mouth on the operator's arm during this procedure.
Useful data
Useful data for cattle are listed in Table 14.2.
Pigs
The various breeds of domestic pig are originally derived from the European wild pig, Sus scrofa, probably crossed with fast-growing Asiatic pigs such as Sus vittatus and Sus indicus. Pure breeds include the Large White, the Landrace, the Saddleback, the Duroc and the Pietrain. However, the majority of commercial breeding pigs are hybrids. These are produced by a number of UK pig-breeding companies and have been developed for high fecundity and the rapid growth of their offspring. Adult sows can weigh up to 250 kg, whereas boars are over 300 kg.
Miniature pigs (mini-pigs) are much smaller in size. Sows of the Yucatan and Göttingen breeds only reach 50–70 kg as adults, which makes them easier to house and manage in a laboratory environment.
Supply
Pigs may be obtained from any supplier. Mini-pigs can be purchased from specialised commercial breeders of laboratory animals. Commercial pigs are best sourced from pig-breeding companies, who maintain herds free from many of the major pig pathogens. It is also possible to source pigs from local farms, but their health status is likely to be less well defined. It is sensible to obtain pigs from clean suppliers when these can be identified. In any event, pigs should be quarantined and faecal swabbing and culture for pathogens such as Salmonella should be undertaken before studies are commenced. It is wise to source pigs from farms that are free from diseases, or where the pigs have been vaccinated.
Behaviour
Pigs are lively, intelligent, gregarious animals that are usually friendly to humans, although newly farrowed sows can be very protective of their litters and adult boars should always be treated with extreme caution. They should be group housed wherever possible, and in a stable group they will develop a dominance hierarchy. If unfamiliar animals are placed together they will normally fight and individual pigs should not be added to a stable group, as they will certainly be bullied and may be killed. It is always best to start with large groups and reduce these in numbers as the pigs grow. However, if mixing is unavoidable then it is better to carry this out on neutral territory at feeding time or at dusk. A tranquillizer, such as azaperone, may be used prior to mixing, in extreme cases.
Pigs rapidly become bored, and a barren environment will lead to stereotypic behaviour patterns, such as ear or tail biting, flank sucking or bar-biting. These vices may be minimised by environmental enrichment in the pen. Pigs have a very keen sense of smell and also well-developed rooting behaviour. If housed outside they will rapidly turn any pasture into a mud-bath by rooting for worms.
Housing
The majority of pigs used in research are kept indoors, either in naturally ventilated or controlled environment buildings. Good building design will encourage cleanliness, as will the provision of suitable bedding. Contrary to popular belief pigs are naturally clean animals, and if provided with sufficient space will defecate only in the coolest, wettest areas, which can then be scraped out or hosed down daily, leaving their bedding area clean and dry. The lying area of the pen should be solid and insulated. It should have bedding, such as sawdust, wood shavings or straw, to provide warmth, comfort and a substrate for rooting behaviour. Pigs will chew and play with straw, aiding digestion and reducing boredom. If no bedding is provided the ambient temperature must be higher and it is likely that more leg injuries will occur. The part of the floor where the pigs are fed and watered should remain un-bedded, and the pigs will use this area for defecating.
Farrowing sows require special accommodation. There is a huge size difference between the sow and her piglets, and with litters of up to 16 it is not uncommon for a sow to inadvertently lie on one or more of her piglets. Farrowing crates and other similar devices designed to reduce this risk are available, and may be used to house the sow from parturition until the piglets are weaned at 4 weeks of age (see Figure 14.7). However these may not be welfare friendly. Newborn piglets require a temperature of 30–32°C, whereas the sow prefers a temperature of 18°C or lower. By restraining the sow in a farrowing crate a heated ‘creep’ area can be provided within the pen to attract the piglets away from the sow when they are not feeding. This creep area should contain a heat lamp or heat pad and a special ‘creep’ feeder.
FIGURE 14.7 Sow in farrowing crate.
Pigs easily become bored and can develop stereotypic behaviour when confined in pens. Environmental enrichment must be provided for indoor pigs and a number of different devices are available, such as heavy-duty plastic footballs, suspended chains and a variety of plastic playthings. Feed-balls are available, which distribute the daily feed ration only if the pig rolls the ball, which encourages activity and exploratory behaviour. Cheap but effective enrichment can be obtained by throwing empty feed-bags into the pen, when the pigs will spend some time tearing these to shreds. Pigs should be group housed where possible, but stable groups are essential to stop fighting. The provision of deep bedding encourages rooting behaviour. In hot weather, a cool shower from a hose tied high above a corner of the pen can provide entertainment and prevent heat stress.
Feeding
Pigs are omnivorous single-stomached animals that will eat a variety of foods. The vast majority of pigs are fed commercial diets, manufactured from ground cereals with added protein, vitamins and minerals. These diets vary according to the age and physiological requirements of the pig. Young pigs are normally fed high-protein pellets, whereas growing and adult pigs are fed restricted amounts of lower protein nuts. Pigs may also be fed directly from the floor in a clean environment, which has the benefit of allowing them to express natural rooting behaviour (see Figure 14.8). The concentrate food may also be purchased as a finely ground, unpelleted meal and fed with water in troughs as gruel.
FIGURE 14.8 Pig rooting for food in straw bedding.
Pregnant sows require a ration containing 12–14% crude protein and will eat 1.8–2.3 kg daily, rising to 2.7 kg immediately before farrowing. Lactating sows should receive a 16–18% protein ration and may eat up to 10 kg daily. Piglets will begin to eat creep feed from about 10 days of age, but it must be fresh to be palatable. Only offer small amounts to start with and clean out uneaten food daily. Creep feed usually has a protein level of over 20%.
Following weaning at 4 weeks of age, creep continues to be fed ad libitum until the piglets reach about 6 weeks. After this, lower-protein feeds are normally given ad libitum until 12 weeks, following which the feed intake is restricted.
Mini-pigs have not been selected for any of the production characteristics of commercial hybrids (rapid growth, high lean/fat ratio and high fecundity), and therefore have different feed requirements in terms of both quantity and quality. In particular they are prone to excess fat if fed ad libitum, and care must be taken not to overfeed them. Special commercial diets for mini-pigs are available.
Water
Water is particularly important for pigs, and must be available at all times. Water deprivation, even for short periods, will cause a rapid increase in blood sodium levels (salt poisoning), which can be fatal. Automatic watering systems are best as they provide water ad libitum. This may be delivered in troughs or bowls (which tend to become dirty) or nipple drinkers (which are much cleaner). Troughs and drinkers need to be above ground to prevent contamination with faecal matter. Buckets and loose troughs are not suitable for pigs as they play with them and soon knock them over. As a general rule adult pigs require 1 litre/10 kg of body weight per day, whereas growing pigs and lactating sows need up to twice this amount. However, these figures are heavily dependent on temperature and feed, so water should always be provided ad libitum.
Environment
Pigs have very few sweat glands and find it difficult to lose heat in hot weather, leading to heat stress, which can sometimes be fatal. Indoor facilities without a cooling plant may find it difficult to prevent overheating in the height of summer. In these buildings cold water from a hose should be sprayed over the pigs if they show signs of heat stress. This is also a form of environmental enrichment, as pigs love to play under a shower of cool water. Pigs directly exposed to the sun can also suffer from sunburn, and shade should be provided in the summer months. Outdoor pigs will make good use of mud wallows.
Although pigs have only a sparse hair covering, their subcutaneous fat deposits help them to keep warm. The optimum temperature for adults is 16°C, which is easily achieved providing the accommodation is well insulated and they have deep-straw bedding and shelter from draughts.
Piglets have a high surface area to body weight ratio and so need high ambient temperatures (28–32°C) for the first few weeks of life. The temperature should gradually be reduced as the pigs age, dropping to 16°C when the pig reaches 80 kg (for Large White pigs).
Relative humidity should be kept between 45 and 65%, but adequate ventilation must be supplied to reduce the levels of ammonia and pathogens in the air, and to dissipate the large amount of heat produced by the pigs. Air speed in lying areas should not exceed 0.2–0.3 m/s for adults and 0.1 m/s for piglets, or excessive cooling occurs.
Breeding
Pigs are prolific breeders and will breed all year round. Large White pigs reach puberty at around 6 months of age and are normally bred from 8 months at about 180 kg. Maiden gilts can be triggered into oestrus by boar contact from 160 days of age.
The oestrous cycle lasts 19–23 days (average 21 days). Oestrus can be detected by pressing down on the sow's back – the back pressure test – when she will stand to be mounted if in ‘heat’. Other signs of oestrus are vulval swelling and vocalisation. Pregnancy may be confirmed by ultrasound scanning from 23 days of gestation. Pregnant sows are normally group housed until 7 days before farrowing, when they are moved into the farrowing crates.
Gestation lasts 114 days, and litter sizes vary between 3 and 18 piglets (average 10.5), dependent on the breed and age of the sow. Litter sizes are maximal for the fifth, sixth and seventh litters and then decline. Prolific commercial sows can produce up to 2.4 litters and rear more than 25 piglets each year. Piglets are weaned from 4–5 weeks. Sows normally return to oestrus 4–7 days following weaning.
Mini-pigs reach puberty at about 4 months of age and have an oestrous cycle of 19–20 days. They have smaller litters than commercial pigs (average of five piglets) and the piglets seldom weigh more than 500 g. Weaning tends to be later (5–6 weeks). The inbred nature of these pigs, coupled with their tendency to become overweight, can lead to infertility problems.
Growth
It is important for piglets to suck colostrum from the sow within 24 h, as no antibodies cross the placenta and intestinal closure takes place after 24 h. If piglets are colostrum-deprived they gain no maternal immunity and are prone to diarrhoea and other diseases.
Piglets are born with minimal body-fat reserves and need to suck frequently in the first 48 h of life to prevent the development of hypoglycaemia. Piglets born indoors, without access to soil, are prone to develop iron-deficiency anaemia and should receive an injection of an iron preparation within the first few days of life. The offspring of commercial hybrids grow very rapidly and should weigh 7–8 kg when weaned. Daily weight gain following weaning is highly dependent on feeding and genotype, but can reach as much as 1 kg/day.
Mini-pigs have similar requirements to standard pigs, but grow more slowly, only reaching 50 kg by about 12 months of age.
Handling
Pigs are easily startled and so should always be approached patiently and quietly. Handling and restraining pigs is usually accompanied by loud squealing, which ceases only when the hold is released. Force should not be used to move pigs, since this will alarm them and cause them to become noisy, obstinate and potentially dangerous. However, they are curious animals and naturally explore their environment. This can be exploited, since they will move along passages quite freely, and a rigid pig board can be used to guide them. Pigs will turn away from solid surfaces (see Figure 14.9). Large pigs may be guided into a crate, or if this is not available they can be restrained by using a rope snare (snatch), placed around the upper jaw behind the canine teeth. The pig pulls away from the snatch, causing the rope to tighten over the nose. Small piglets may be picked up, providing the abdomen is always supported. They should not be picked up by the hind legs alone. Larger piglets can be tucked under one arm, with the weight supported by the other arm placed under the belly. A foreleg can be held to provide additional restraint.
FIGURE 14.9 Moving a pig using a pig board.
Pain and stress recognition
Pigs in pain will show a decrease in their normal inquisitive behaviour, becoming listless and quiet. However, they may show aggression on being handled, so care should be taken. In white pigs the skin may show marked colour changes (pallor or cyanosis) and there may be piloerection of the sparse hair coat. In a group the sick pig will fail to thrive and may develop abnormal behaviour patterns, such as urine sucking.
Common diseases and health monitoring
Pigs are prone to a number of diseases (Table 14.3), some of which are notifiable under the UK Animal Health Act 1981, such as classical swine fever (CSF) and foot and mouth disease (FMD). Purchasing from sources of defined health status, using tailored vaccination programmes and applying rigid biosecurity measures, will control most pig diseases. The Federation of Laboratory Animal Science Associations (FELASA)8 has published recommendations for health monitoring programmes in experimental pigs.
Table 14.3 Diseases of pigs.
| Disease | Comments |
| Zoonoses | |
| Salmonella species | Subclinical infections in many herds. Monitoring is conducted on pigs at abattoirs. |
| Streptococcus suis Type 2 | Carried asymptomatically in the oral cavity. Causes meningitis under certain circumstances. Classified as a zoonosis, but transmission to humans is rare. |
| Influenza virus | Various strains of influenza A endemic in most UK pig herds. Usually mild in pigs, but can be serious. Transmission to humans is possible, but rarely results in disease. New strains appear occasionally, which cause pandemic disease. |
| Erysipelothrix rhusiopathiae (erysipelas)* | Common cause of systemic disease in pigs. Can also cause skin disease in humans. |
| Clinical diseases | |
| Mycoplasma hyopneumonia* | Causes enzootic pneumonia (EP). Widespread in UK pig herds. Most commercial herds vaccinate piglets. |
| Actinobacillus pleuropneumoniae (APP)* | Common. Protected against by vaccination. |
| Toxigenic Pasteurella multocida* | Causes atrophic rhinitis (AR). Common. Protected against by vaccination. |
| Brachyspira hyodysenteriae | Swine dysentery. Seen in older pigs. |
| Clostridium* and E. coli* | Neo-natal diarrhoea |
| Enteric coronavirus | Transmissible gastroenteritis (TGE) |
| Porcine parvovirus* | Affects fertility |
| Porcine reproductive and respiratory syndrome* | Affects fertility |
| Leptospirosis | Many pig herds serologically positive, but few exhibit any clinical signs of infection. |
| Haemophilus parasuis* | Causes Glässers disease. |
| Circovirus 2 | Post-weaning multisystemic wasting syndrome (PMWS). Affects growing pigs 10 weeks or older. Virus causes immunosuppression, so previously subclinical diseases become clinical. Endemic in UK pig herds and sourcing pigs free of PMWS is very difficult. Mortality can be high. |
| Endoparasites | Uncommon in indoor pigs. |
| Ectoparasites | E.g. mange mites and lice. Can cause skin irritation and self-mutilation |
| *Vaccines are licensed for use in pigs to protect against these diseases. | |
Techniques
Intravenous injections
Pigs lack easily accessible superficial veins and so intravenous injections can be difficult, especially in very small piglets. The marginal ear vein is the vein of choice, as the jugular vein is too deep to be certain of needle placement. Local anaesthetic cream (e.g. EMLA, AstraZeneca) can be applied over the site of the ear vein 15 min before injection, to desensitise the skin. Less pain is caused if flexible cannulae are used, rather than rigid needles.
Intramuscular administration
Care must be taken if giving intramuscular injections that the agent is not injected into the thick subcutaneous fat layer by mistake, or absorption of the drug will be delayed and the expected effect will not be achieved. The usual site for i.m. injections is the musculature of the neck and an 18 G, 40 mm needle should be used in adult pigs. For ease of administration the needle may be attached to the syringe by a long, flexible extension line to avoid the need for prolonged restraint.
Subcutaneous administration
Since pigs have a thick layer of subcutaneous fat immediately below the skin, subcutaneous injections in most places may simply end up in the fat layer. Subcutaneous injections may be given into the skin at the base of the ear, or into the fold of skin immediately in front of the hind leg.
Anaesthesia
Anaesthesia in the pig is generally straightforward, but there are some unusual features that should be borne in mind. The most satisfactory method of inducing anaesthesia is to administer an injectable anaesthetic agent intravenously, which is facilitated by prior sedation. Doses for anaesthetic and analgesic drugs can be found in Table 9.3f.
Food should be withheld for 8–12 h before anaesthesia to prevent vomiting (1–3 h in neonates). Water must be available at all times up until an hour before the anaesthetic is given.
Respiratory depression and/or apnoea are common complications of surgical anaesthesia in the adult pig, particularly if it is very fat. The head should be kept at as natural an angle as possible to prevent pressure on the larynx. If the pig is not intubated it is essential to ensure that the airway is kept clear and laryngospasm is prevented. Applying pressure on the vertical ramus of the mandible to push the jaw forward, and extruding the tongue, will help to prevent obstruction. Administration of atropine (0.3–2.4 mg depending on the size of the pig) to dry secretions will also help.
Inhalation agents (isoflurane or sevoflurane) are ideal for maintaining anaesthesia in pigs, following induction with injectable agents. Endotracheal intubation is straightforward in young pigs, but can be difficult in larger pigs. A larnygoscope with a very long blade is required to visualise the larynx in adults. The pig trachea is narrower than might be expected for an animal of its size and there is also a pharyngeal diverticulum, which can cause confusion. It is common to intubate adult pigs in dorsal recumbence, but intubation in ventral recumbence is also possible. The tube needs to be long and a rigid stylet is very helpful.
Pigs have poor thermoregulation mechanisms and can develop hyperthermia during prolonged anaesthesia. Some strains of pig also have an inherited biochemical myopathy known as porcine malignant hyperthermia. In these pigs, when anaesthesia is induced, a contracture of the skeletal muscles occurs, the pig becomes rigid and its temperature begins to rise. The strains of pig most commonly affected are the Poland–China, the Pietrain and some lines of Landrace and Large White. However, genotyping has allowed breeding companies to select against this trait and they will normally be able to supply pigs free of this condition, if requested.
Useful data
Useful data for pigs are found in Table 14.4.
Table 14.4 Useful data: pigs.
References and Further Reading
References
1. Home Office (2011). Statistics of Scientific Procedures on Living Animals: Great Britain 2010. London: The Stationery Office. www.official-documents.gov.uk/document/hc1012/hc12/1263/1263.asp
2. National Research Council (1994). Nutrient requirement for chickens. In Nutrient Requirements of Poultry, 9th edn, pp. 19–34. Washington DC: National Academies Press
3. Federation of Laboratory Animal Science Associations (2007). Euroguide on the Accommodation and Care of Animals used for Experimental and Other Scientific Purposes. London: RSM Press
4. Rushen J, Boissy A, Terlouw EMC and de Passillé AMB (1999). Opioid peptides and behavioral and physiological responses of dairy cows to social isolation in unfamiliar surroundings. Journal of Animal Science 77: 2918–24
5. Price EO, Adams TE, Huxsoll CC and Borgwardt RE (2003). Aggressive behavior is reduced in bulls actively immunized against gonadotropin-releasing hormone. Journal of Animal Science 81: 411–15
6. Tucker CB, Rogers AR and Schutz KE (2008). Effect of solar radiation on dairy cattle behaviour, use of shade and body temperature in a pasture-based system. Applied Animal Behaviour Science 109: 141–154
7. Kendall PE, Nielsen PP, Webster JR, Verkerk GA, Littlejohn RP and Matthews LR (2006). The effects of providing shade to lactating dairy cows in a temperate climate. Livestock Science 103: 148–57
8. Federation of Laboratory Animal Science Associations (1998). FELASA recommendations for the health monitoring of breeding colonies and experimental units of cats, dogs and pigs. Laboratory Animals 32: 1–17
Further reading
1. Allen MJ and Borkowski GL (1999). The Laboratory Small Ruminant. Boca Raton, FL: CRC Press
2. DEFRA. Codes of Recommendations for the Welfare of Livestock: Poultry, Pigs, Sheep, Goats, and Cattle. All documents available from www.defra.gov.uk/publications/tag/code-of-recommendation/
3. Federation of Laboratory Animal Science Associations (2000). FELASA Recommendations for the Health Monitoring of Experimental Units of Calves, Sheep and Goats. Laboratory Animals 34: 329–50
4. Hu C, Cheang A, Retnam L and Yap EH (1993). A simple technique for blood collection in the pig. Laboratory Animals 27: 364–7
5. Pattison M, McMullin P, Bradbury JM and Alexander D (2008). Poultry Diseases, 6th edn. Philadelphia: Elsevier
6. Rispat G, Slaoui M, Weber D, Salemink P, Berthoux C and Shrivastava (1993). Haematological and plasma biochemical values for healthy Yucatan micropigs. Laboratory Animals 27: 368–73
7. Webster J (2011). The UFAW Handbook on the Management and Welfare of Farm Animals, 5th edn. Chichester: John Wiley and Sons