ALAT Chapter 26 Swine PDF

ALAT Chapter 26 Swine • The use of swine (pigs) in biomedical research is well established. In general, two types of swine are used in research: the domestic swine, produced for agricultural purposes, and miniature swine (minipigs). • Pigs have typically been used for studying exercise physiology,...

ALAT Chapter 26 Swine • The use of swine (pigs) in biomedical research is well established. In general, two types of swine are used in research: the domestic swine, produced for agricultural purposes, and miniature swine (minipigs). • Pigs have typically been used for studying exercise physiology, nutrition, atherosclerosis, diabetes, and transplantation as well as surgical training. With the development of specific pathogen-free minipigs, work with these animals in research has expanded to include toxicology, reproductive, and pharmacological studies in support of drug development. Their relatively long lifespan makes them particularly appropriate for studies of cardiovascular disease, gerontology, and toxicology. Hairless strains have been developed for use in skin sensitivity studies. • Minipigs were purposely developed as research animals. Minipigs have been selectively bred for their small size and docility. • Domestic swine are often used for short-term studies in which maturity or development is not important, but their rapid growth and large size limit their usefulness for chronic studies. Young animals are normally used, since these breeds can weigh more than 100 kg by the time they reach sexual maturity and may be difficult to handle. • Standard handling and dosing procedures should be adapted in each facility, and positive interaction is crucial to minimizing stress for both caretaker and animal. Staff should be specifically trained in handling this species. Taxonomy & Breeds • The domestic pig’s scientific name is Sus scrofa domestica. • Domestic Swine: Of the many breeds of domestic swine, the Yorkshire, Duroc, and Landrace are the breeds commonly seen in research facilities. • Minipigs: • US: The Yucatan, Hanford, and Sinclair are the most frequently used breeds of minipigs in the United States. • Europe: The Gottingen minipig is the most frequently used breed in Europe, and is also available in the US. • Micro-Yucatan minipigs have the same origin as the Yucatan minipigs. Anatomy & Physiology • Why pigs? The internal organs of a pig are similar to human organs. Adult domestic pigs weigh about the same as humans, and their organs are about the same size. Their skin, teeth, upper gastrointestinal tract, heart position, and blood supply are very similar to those of humans, and so are their nutrient requirements. Mini and micropigs differ from domestic pigs mainly in their smaller body size, and earlier sexual maturation. Figure 26.1 shows the size difference between the domestic pig and the miniature breeds. • Pigs have a firm nose, which is reinforced with cartilage. The nose is used to explore the environment by pushing and lifting objects. This exploration with the nose is known as “rooting” and is a normal behavior that should be encouraged with appropriate environmental enrichment such as chains and heavy balls. • Pigs have hooves with four toes. Facilities housing swine should ensure that the flooring is nonslip, as pigs do not like to be on slippery surfaces, such as wet concrete. A mature boar of domestic, mini, or micro breed has two upper and lower canine teeth, known as tusks. Mature barrows (castrated males) may also have tusks. Boar tusks have a razor-sharp edge for slicing, and can be a danger to personnel and other animals. For safety, tusks should be trimmed periodically, as they grow continuously through life. Sows may have canine teeth, but they are less well developed than those of boars. Piglets may also need to have their neonatal ‘needle teeth’ trimmed. Trimming or grinding down these teeth reduces piglet facial lacerations caused by animals fighting for teat access. Blunting these teeth has also been shown to reduce lacerations to the mother’s udder caused by sucking piglets. Sexing • An uncastrated male pig is called a boar, and can be identified by the presence of testes and a penis. • Females are identified by the presence of a vulva. A female pig that has not yet produced a litter is called a gilt; a female that has already produced a litter is referred to as a sow. • Young are called piglets. Reproduction The sow’s breeding season extends over the whole year, except when she is pregnant or suckling young piglets. Gilts can generally be bred at 6 to 7 months of age. Estrus is indicated by a vaginal discharge of mucus accompanied by swollen, congested external genitalia and by mounting behavior. Handlers detect estrus as receptivity to breeding when they press a hand on the female’s back and the animal assumes a breeding stance. Increasing the feed allowance 7 to 10 days before breeding is thought to lead to an increased litter size. Absence of estrus 21 days after mating provides reasonable evidence that the animal is pregnant. Pregnancy can be confirmed at 60 to 90 days of gestation by radiography. Gestation lasts approximately 112 to 115 days, and litter sizes are from 8 to 15 piglets. In pigs, the term “farrowing” is used to describe giving birth to a litter of piglets. Laboratory sows are usually isolated in a pen to farrow. The pen floor should be lightly covered with chopped straw, sawdust, shavings, or ground corncobs. To help prevent the sow from smothering the baby pigs by laying on them, guardrails should be installed above the bedding and away from the wall of the pen; piglets can move under the rails to safety. Newborn pigs are very susceptible to chilling. An extra heat source, such as a heat lamp, may be placed over the pen to prevent the development of hypothermia (low body temperature). Behavior Though they are social animals, swine have little herding instinct and can behave unpredictably. They can become aggressive with little warning. With routine handling, how ever, domestic pigs acclimate to humans and can become docile. They are intelligent, and will cooperate in training for food rewards. Pigs have extremely strong jaws; their principal defense is their teeth. They use their teeth to test objects in their environment, first nibbling and then biting. When holding an object by their teeth, they may pull on it or shake it with their head. When you are standing in a pen, a pig is likely to nibble on your boot or trouser. Shoo the pig from you or move away from the pig, so that it does not grab a strong hold on your clothing. Otherwise you could lose your footing, and perhaps get bitten, as the pig tests your clothing more strongly. Pigs are very strong, and one rushing to get past you can knock you off your feet. When you are among large pigs, it is important to remain standing to keep your hands and head safe from being bitten. If you have to crouch, perhaps to fix something in a pen, either the pen should be unoccupied or you should have a second person standing with you to keep pigs from mobbing you. Socializing: Minipigs and microswine are social animals. They are easily socialized with humans and respond to gentle handling. It is very important for the staff to socialize with the animals to make them more comfortable with their environment and with their caretakers. Swine quickly become used to their daily routines. They respond well to positive reinforcement and like to be rubbed or scratched on the belly and behind the ear. If single housed, gentle interaction with caretakers should be included as a part of the animal’s enrichment program. Housing: Pigs prefer a clean environment, and will often defecate in a corner of the pen in a wet area, typically near their waterers. Their feeders should be placed away from the waterers to minimize soiling of their feed. Vocalizing: Swine are very vocal when handled; such vocalization does not usually indicate an expression of pain or discomfort. They are usually very excited at feeding time and vocalize until they are fed. Fighting: Pigs establish dominance very early in life; fighting can be a problem in group-housed animals, particularly young boars. Uncastrated males of some breeds may be particularly aggressive and may resist handling. When domestic pigs are picked up or physically restrained, they may struggle and will scream loudly until released. Personnel exposed to such screams frequently or for prolonged periods should wear hearing protection, as mandated by their institutional health and safety program. Handling Handling and restraint procedures for minipigs are quite similar to those used for laboratory dogs. Minipigs and microswine should be handled gently; they can be held on one arm like a child. They enjoy being petted. When approaching these pigs, technicians should bend down or crouch because this approach is less intimidating for the animal. Minipigs and microswine are easily trained to cooperate with examinations and manipulations; food treats are an important motivator. Domestic pigs purchased from farms are generally not well socialized to humans and so are less easy to manipulate. Restraint of domestic swine may require two or more staff members, depending on the size of animal, the type of procedure, restraint device, and animal’s cooperation. Restraint • Domestic pigs can be trained to cooperate with certain physical restraint methods, though such training requires more effort than for minipigs. Restraint is less stressful for trained animals. A common method of restraint for any pig breed is a sling or hammock that can comfortably immobilize pigs of sizes typically used in research. The sling suspends the animal off the floor, with its legs dangling through holes in the bottom of the sling. • Panepinto Sling® uses a crank mechanism that raises the pig from the floor to an appropriate working height and can be operated by one technician. Pigs can be trained to cooperate by walking onto the sling and to accept being raised off the floor. • Another restraint method common in the research environment is the Terris confinement stand. These stands are constructed of metal panels that form a small, pen-like enclosure that confine a standing pig without total immobilization. A pig can be trained to enter the stand and then return to its pen after the completion of a procedure by offering food rewards to the pig during the procedure. • A V-trough is typically used to restrain small pigs on their backs for nonpainful procedures, such as blood collection from veins in the neck. This method of restraint usually requires two or more staff members in addition to the individual performing the technical manipulation. • The snare method can be used to restrain larger domestic pigs in a standing position. A rope or metal noose is inserted in the pig’s mouth and then tightened around its snout, so the pig is restrained by the upper jaw. The pig responds by standing with a backward-leaning stance and screaming. The handler can induce the pig to back up into a corner, where it can be controlled more easily. Restrained by a snare, the pig generally stands still for nonpainful procedures, such as blood collection. Improper or excessive use of this method can cause bleeding of the gums and damage to the animal’s teeth. This method was originally developed for farm pigs, and it is too forceful for restraining frequently handled laboratory swine, especially minipigs and microswine. Identification Methods • Pigs are most commonly identified with an ear tag but may also be microchipped at the base of the ear. • Ear tattooing and notching are other permanent method of marking pigs, but both procedures can cause stress to the animal and should be avoided where possible. Husbandry Pigs should not be housed in cages unless absolutely necessary for the procedure, and then only for a short time. Minipigs and microswine are housed indoors in a controlled environment. They are usually housed in groups (with the exception of mature boars), but can be housed individually if necessary for the study. Males and females are housed in separate pens. To minimize stress when establishing their new hierarchy, the animals should be housed with the same individuals who shared their pen prior to shipment, at least initially. If the minipigs are housed in individual pens, they should be able to have snout contact through pen dividers or at least be able to see and hear other pigs. Pigs in adjacent pens will nose each other through their pen bars. If the pen walls have horizontal bars, the walls should be at least 4 to 5 feet high to prevent animals climbing out of the pen. Although pigs are not climbing animals, horizontal bars allow them a foothold as they rear up against the wall. Pig pens with vertical bars can be shorter; 3½ feet is adequate. To prevent competition for feed in group-housed animals, adequate access to water and feeder space must be provided so that all animals can feed at the same time. Group sizes should be limited to 10 to 15 animals to promote a stable social hierarchy. If possible, avoid moving the animals to different groups, as this will cause fighting until a hierarchy is established. Designs for indoor swine facilities are usually developed to meet specialized needs, such as breeding, farrowing, housing young pigs, or providing environmental control of temperature and humidity. Fences, pen dividers, and gates should be well constructed of durable material. Water bowls and feeders must be secured to the pens to withstand rooting behaviors. Runs designed to house dogs are frequently used to house smaller pigs. If slatted or wire mesh floors are used, make sure that the spacing of the slats or grids is not large enough to cause hoof damage. Nonslip concrete floors, if properly constructed, provide adequate drainage and permit the easy collection of waste. Some facilities provide bedding (straw, shavings), while others just house animals on the concrete. A good supply of water under high pressure is essential for flushing concrete surfaces and to effectively clean pens. Hoof trimming is an essential component of swine maintenance. Even animals housed on concrete will need their feet trimmed periodically to prevent overgrowth of hooves. Difficulty walking, lameness, and diseases of the joints and hooves are possible complications of inadequate hoof maintenance. Good restraint (sometimes sedation) and commercial hoof trimmers are essential for foot trimming. Housing for domestic swine is quite different from housing for minipigs. In moderate climates, domestic swine may be housed outdoors. One of the chief advantages to this type of housing is the lower initial cost. Outdoor facilities usually consist of portable shelters or open-front sheds placed on concrete, which provide a dry, draft-free bedding area. Fencing used to enclose outside pens should be either chain-link or panel type; woven wire is easily destroyed by adult pigs. During the summer, access to a cool place should be provided by shade trees, portable shade stands, or cooling ponds (not mud wallows). Diet Pigs are omnivorous and are always interested in eating, especially if they have to compete for the feed. A number of diets formulated specifically for laboratory swine, both full size and miniature, are readily available from commercial suppliers. Swine maintained in a laboratory environment should not be fed more than 2% of their body weight daily; some minipigs require less. Obesity in pigs is extremely difficult to correct, and should be avoided. If pigs are maintained outdoors, feed quantities should be increased slightly; pigs generally have more room to exercise outdoors, which usually results in an increased metabolic rate. Minipigs and microswine are generally fed a low-calorie diet to prevent obesity. Minipigs can be fed from a bowl or trough. As with domestic swine, adequate space for feeding and watering must be provided. This will prevent competition among group-housed animals. At least 0.25 meters (10 inches) of trough space per adult animal should be available. Alternatively, the pigs can be fed from a clean floor to reduce competition. Young animals are usually fed twice a day; animals older than 7 months are generally fed once daily. Automated drinking systems are recommended to make sure that water is available ad libitum. Water nipples should be positioned approximately 1 inch below the shoulder height of the pigs, which makes the animals lift their heads slightly to drink. Nipple height must be adjusted as the pigs grow. For minipigs, the nipple should provide at least 0.5 to 1.0 quart of water per minute. Water dishes, if used, should be installed 0.1 meters (3 inches) above the floor. If water is provided opposite to the feeding area, the minipigs will keep the feeding area clean, since minipigs use wet areas for defecation and urination. Environmental Enrichment Pigs respond differently to environmental enrichment than other research animals. Pigs become bored very easily and will ignore enrichment materials that lose their novelty, so toys should be rotated regularly. Similarly, swine will develop negative behaviors much more readily if they have had environmental enrichment that is subsequently removed, or if they are moved to an enclosure that lacks it. Environmental enrichment may include heavy balls that pigs can roll around the pen and toys suspended from the pen dividers. A substrate, such as autoclaved straw or hay, is considered environmental enrichment because it allows the pigs to root; it has the added advantage of providing insulation. Straw has been shown to reduce aggressive behaviors such as tail biting, if provided at an early age. If the pigs are enrolled in oral dosing studies, straw and hay are generally not used because they may increase gastric emptying time. Straw is also important during farrowing, and sows should be provided material at least 24 hours before birth so they can address their strong motivation to nest. Signs of Pain, Distress, or Illness Pigs in pain are often unwilling to move and may become aggressive. They will squeal when a painful area is touched. An observant technician may also detect a change in an animal’s behavior and gait. Because pigs often sleep long hours in close contact or piled together, an animal that is ill may not be easily detected until the others get up and walk about. Check the animals at times when they are active and eating. Euthanasia • Pigs in research should be euthanized by an injection of a lethal dose of barbiturate. • The AVMA Guidelines for the Euthanasia of Animals has also approved the use of cardiac injection of potassium chloride while under anesthesia or a penetrating captive bolt. • As with other laboratory animal species, death must be verified. Carcass disposal should be according to the facility’s guidelines.