Biology and Medicine of Swine

Introduction

Domestic and miniature swine (Sus scrofa domestica) are widely used in biomedical research either as a general large animal model or as a model specifically based upon their comparative anatomy and physiology. This manuscript provides an overview of the use of swine as laboratory animals. More comprehensive information is available in textbooks [1-7].

Biology

Basic Biological Normative Data [1,3].

Figure 1. Average whole body weights of fifteen female Yucatan Micropigs (Charles Rivers, Windham, ME, USA) fed 2,600 kcal per day from 7 - 14 months of age. Adapted from [8].

Figure 2. Average normal mean non-invasive blood pressures of twenty female Yucatan Micropigs (mean weight 22kg, Charles Rivers, Windham, ME, USA) while resting in a hammock-sling. Data are shown as mean (+/- SE) plotted over time in the hammock. Adapted from [9].

Figure 3. Average normal mean heart rates of twenty female Yucatan Micropigs (mean weight 22 kg, Charles Rivers, Windham, ME, USA) while resting in a hammock-sling. Data are shown as mean (+/- SE) plotted over time in the hammock. Adapted from [9].

Anatomy

Swine have several unique anatomic characteristics, mainly found within the digestive system. The stomach has a muscular outpouching, the torus pyloricus, in the region of the pyloric sphincter. The branching of the mesenteric vessels is located in the subserosa of the small intestine instead of the mesentery. The cecum and most of the large intestine is coiled into a spiral colon in the left upper quadrant of the abdomen. Other abdominal organs such as the liver and kidney are very similar to the human.

Both sides of the lung have apical, middle and diaphragmatic lobes with an additional accessory lobe in the right lung. The heart is generally like that of the human, with the exception of the left azygous vein, which enters the coronary sinus. The coronary vasculature is very similar to that of the human.

The female reproductive tract is bicornuate. The uterus is histologically more similar to the human than many other species except the non-human primate. The pig has epitheliochorial placentation and virtually no immunoglobulin is transferred crossplacentally.

The male urogenital tract has a corkscrew shaped penis tip and a preputial diverticulum which makes it difficult to catheterize males in a retrograde manner. The accessory sex glands are similar to those of humans.

More complete information is available in anatomy texts and review articles [1,10-12].

Nutritive Requirements

Commercial diets for farm pigs usually contain antibiotics and other supplements to increase weight gain. Commercial diets are available for miniature breeds, which are more specific to the needs of laboratory animals and may be used for domestic breeds. The National Research Council (NRC) has published the complete nutrient requirements for swine [13]. Iron deficiency anemia may occur in nursing piglets unless they are supplemented with 100 - 200 mg of iron dextran IM within 48 hours after birth. Most swine used in research are between 10 - 80 kg and require approximately 1000 - 2575 gm of food per day and an estimated metabolizable energy intake of 3265 - 8410 kcal/day in that weight range. Swine require approximately 2.5 liters of water per kg of food consumed per day and water restriction may result in a neurological syndrome referred to as "salt poisoning" or sodium toxicosis. Salt poisoning may also occur due to an increased sodium ion intake. Affected swine develop an eosinophilic meningoencephalitis leading rapidly to convulsions and death if they are not immediately rehydrated [1,14].

Clinical Pathology and Hematology Data

Hematologic and clinical chemistry data may vary among breeds and among animals of different ages and gender within a breed. Comprehensive charts of these values are available [1,3,14].

Husbandry and Management

Husbandry and care of swine should be appropriate for their anatomic, physiologic and behavioral characteristics as well as for vendor herd health status [1,3,14]. Miniature swine available from commercial vendors of laboratory animals and swine from quality herds reared for meat production receive preventative treatments for ecto- and endoparasites and vaccinations against common swine diseases at appropriate ages and intervals. Swine reared for meat production are readily available, but health status among herds tends to be highly variable. Therefore, swine from different vendors should be housed separately.

Pens are more suitable for housing swine than cages. Pens can be made using a combination of concrete walls with fencing of galvanized or stainless steel. Sturdy construction should be used since pigs are strong and can be destructive either by chewing, rubbing against caging, or by rooting. Caging should be free of any loosely fitted areas or surfaces that can be manipulated by swine to prevent injuries.

Special consideration should be given to the choice of pen flooring. Swine may be kept on either contact or raised flooring. Contact flooring should have a rough surface to provide secure footing or be covered with wood chip bedding. Bedding material provides an outlet for rooting and nesting behaviors, but makes sanitation more labor intensive and may be eaten if swine are fasted for surgery. Raised flooring is satisfactory in most laboratory environments and is easier to sanitize since generally no bedding is provided. Grid floors are made of plastic coated metal or fiberglass and can be designed in either a diamond structure or as parallel bars. Slatted fiberglass floors with grit are ideal since they provide hoof wear and are lightweight for easy sanitation. A slat width of 1.75" (4.4 cm) with a space of 0.25" (0.64 cm) between slats is ideal.

Automatic waterers are preferred to water bowls since they provide a constant source of uncontaminated water which cannot be spilled. Swine can develop a neurologic condition referred to as "salt poisoning" if water deprivation results in dehydration. Feeders should be firmly secured to the cage side or floor and made of a smooth material such as stainless steel or Teflon that is easily cleaned. Feeders should be sturdy and able to withstand being chewed or stood upon during the excitement of feeding. Swine will defecate at the opposite end of the cage from where they are fed. Consequently, swine should be fed and watered separate from where they defecate.

Pigs may be housed individually or in small groups. Space recommendations for housing laboratory swine have been published in the National Institutes of Health Guide for the Care and Use of Laboratory Animals [15] and the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching [16]. They are highly social animals and need to have aural, visual and olfactory contact with other members of their species. Dominance fighting will occur if inadequate space is provided or if new animals are mixed into an established social group. Laboratory swine are often single housed and should be able to see, hear and smell each other. They also interact with people who care for them, and daily positive contact should be encouraged. Providing swine with objects that they can manipulate such as balls or chains helps to satisfy their need to chew and root. Items of environmental enrichment should be easily sanitized and selected to prevent damage to the cage or injury to the animal. To maintain interest in the item and prevent soiling, toys should be available for a limited period daily.

Excreta should be removed from pens daily. If bedding material is used, it should be changed once or twice weekly with daily spot cleaning of soiled bedding performed between changes. Cages without bedding should be hosed once or twice daily. Animals should be taken out of the cages during cleaning to prevent chilling. However, swine willingly accept baths and can be cleaned with mild soap and warm water. Pens should be thoroughly sanitized with a suitable disinfectant every 2 weeks. Disinfectants should be thoroughly rinsed and flooring dried before allowing animals to be returned.

Restraint

Use of a humane restraint sling is recommended for research swine since it is much less stressful than agricultural methods of restraint such as snout snares or suspending them by their rear legs (Fig. 4). Swine respond well to positive reinforcement and gentle handling and can be trained to walk out of their pens into a lowered sling. Acclimation and training to any research equipment should be standard procedure and can be readily achieved by using food rewards. Smaller animals (up to 20 kg) can be held in a handler’s arms like a dog. Large swine can be driven in the appropriate direction by walking behind them. Hand-held panels can be used to herd or restrain swine against the side of the cage.

Figure 4. Yucatan pig in a humane restraint sling.

Suppliers

Miniature pigs are generally procured from commercial vendors of laboratory animals, while farm pigs are generally procured from local farm production units. Care should be taken to ensure that suppliers offer high quality, healthy animals by veterinary review of their health care program. Website addresses of major suppliers and informational databases are located at the end of the references.

Vaccination Programs

Vaccination programs are generally specific for the region and herd of animals rather than being universally recommended. The term Specific Pathogen Free (SPF) is a proprietary term for swine referring to disease conditions that stunt growth in agricultural production. It does not represent that swine with an SPF designation are pathogen free. Laboratory animal facilities will generally not have to vaccinate animals on site if they are purchased from a supplier with an adequate health program and they are not maintaining breeding stock.

Pathogens against which piglets are commonly vaccinated include Leptospira, Erysipelas, Pasteurella, Bordetella. Piglets are generally vaccinated at four weeks of age with a second booster given 2 - 3 weeks later. Adult breeders are commonly vaccinated annually for: Parvovirus, Leptospira, Transmissible Gastroenteritis, Erysipelas, Bordetella, Pasteurella and Colibacillosis.

Anesthesia, Analgesia, Euthanasia

Complete information on anesthesia, analgesia and euthanasia for swine used in research is available in several textbooks [1,3,14,17,18]. The chart below lists commonly used agents.

Ketamine and tiletamine/zolazepam (Telazol) are the most commonly used chemical restraint agents. As sole agents they do not provide sufficient analgesia for performing surgery. When combined with other agents, they are frequently used as preanesthetics. The physiologic effects of administering such agents should be considered when using them in a research protocol. When using injectable agents for a procedure, it is best to administer them as infusions rather than repeated bolus injections. For general anesthesia, isoflurane is the agent of choice for most protocols.

It is best to use preemptive analgesia when performing major surgery in swine. Use of epidural morphine for abdominal procedures is highly effective. Administration of an opioid, such as buprenorphine, and infiltration of the incision with a local anesthetic is a standard methodology of providing preemptive analgesia.

Swine are susceptible to cardiac arrhythmias and cardiac arrest when manipulation of the heart is performed. A sudden death syndrome may also be encountered when swine are stressed. Treatment and prevention of cardiac arrhythmias is complex and discussed in depth in other textbooks [1,6,18]. Antiarrhytmic agents such as lidocaine infusions, bretylium and amiodarone should be available during cardiovascular procedures, as well as defibrillators.

Euthanasia may be accomplished by standard techniques used in other large animal species [18]. An IV overdose of pentobarbital (>150 mg/kg) or pentobarbital containing euthanasia agents is the preferred technique. While under general anesthesia, terminal exsanguination or administration of KCl IV are also acceptable. In larger animals it may be advisable to administer a tranquilizing or anesthetic agent first in order to facilitate IV access.

Detailed discussions of the use of anesthetics and analgesics may be found in other reference textbooks [1,3,17,18].

Diseases and Medicine

Infectious Diseases

Pigs obtained for use in research should be purchased from herds with a defined health status. Once these pigs are purchased, good husbandry practices in concert with isolation of incoming animals of undefined health status will limit the incidence of infectious diseases in a research environment. Despite the management paradigm which supports low disease incidence, people supporting the use of swine in research need to be familiar with the classic diseases that afflict swine with an emphasis on those diseases that can emerge when animals become stressed by experimental manipulations. For more detailed descriptions of the diseases discussed, the reader is referred to published textbooks [3,14,19].

Key to management and treatment of diseases in swine is the prompt identification that the animal is ill. The animal’s behavior as observed in solitude, and in interactions with caretakers, defecation and eating patterns, respiration, and posture should be evaluated daily. Pigs which are systemically ill, or are experiencing lameness will not rise from a resting position even for the promise of food. A pig with mild disease may eat, but demonstrates a less enthusiastic response to a food offering and/or may discriminate against food, i.e., will eat a doughnut, but not pig chow. Respiratory illnesses can be obvious with mucopurulent nasal and ocular discharge, coughing, sneezing or more subtly displayed with a dog-sitting posture and labored respirations observable only when the pig is at rest. Gastrointestinal diseases can be relatively easily identified by noticing a change in the animal’s defecation patterns typically leaning towards diarrhea or a loss of weight. The tone and texture of the pigs skin can vary greatly by breed, however, it should be free of lesions and the color of the mucosa and skin should reflect adequate cardiovascular perfusion.

Respiratory Disease

Infectious agents that initiate respiratory disease are often found endemically in herds of swine. Transmission occurs via aersolization of infectious particle and/or by contact. Control of clinical symptoms and disease spread is dependent on managing population density, providing adequate ventilation and temperature control and minimizing stress. In addition to creating complications with general anesthesia, the impact of the following diseases on studies of the respiratory and cardiovascular system can be profound.

Atrophic Rhinitis is mutifactorial disease caused predominately by Bordetella bronchiseptica acting at times, in concert with Pasteurella multocida. Clinical symptoms of sneezing, coughing and mucopurulent nasal discharge manifest in young pigs between the ages of 3 - 8 weeks. This can then be followed by atrophy of the turbinate bones, which may be accompanied by distortion of the nasal septum, and shortening or twisting of the upper jaw. Separate Bordetella infections have a mild and transient impact on the turbinates, while those infections that involve Pasteurella tend to have a severe and permanent impact. Key to control is adequate vaccination. Clinical symptoms can be managed with antibiotic therapy.

Inclusion Body Rhinitis, which is caused by cytomegalovirus, is a disease found throughout the world with clinical symptoms inapparent in pigs greater than 3 weeks of age. In these young pigs, a moderately severe rhinitis and conjunctivits can occur. Clinical sequelae in pregnant sows include unexpected fetal and piglet death. The virus can cause latent infections with shedding of the organism occurring even with circulating antibodies present. Control of stress discourages resurgence of the virus.

Mycoplasma hyopneumoniae is probably the most common cause of chronic pneumonia in swine with most conventional herds being affected. Younger pigs may be symptomatic, however, most clinical signs are not observable until pigs are 3 - 6 months of age. The disease in its uncomplicated form creates a slowed growth rate and a chronic cough that becomes exacerbated with exercise. The disease is chronic in nature and occasional acute respiratory signs can occur. In infections complicated by concomitant respiratory pathogens such as Pasteurella, fever and labored breathing can occur. The most effective form of disease prevention is to only purchase pigs from herds free of the disease. Pigs are capable of mounting an immune response and recovering from the disease without assistance of antibiotics, however, antibiotics help to reduce clinical symptoms and control the complicating bacterial infections to which the disease predisposes the animal.

Mycoplasma hyosynoviae frequently colonizes the upper respiratory tract of swine. In pigs 12 - 24 weeks of age it may produce an acute arthritis, which may develop into a chronic condition. Pigs may be predisposed to development of clinical arthritis by poor limb comformation or trauma. Treatment with tylosin or lincomycin may be effective, especially during the acute phase of the infection. Chronic arthritis or osteochondrosis does not respond well to any treatment.

Pasteurellosis is most commonly seen in pigs as a complication of mycoplasmal pneumonia although it can also result from other diseases that insult the lungs. The causative organism, Pasteurella multocida, is a common inhabitant of the upper respiratory tract of swine. It produces an exudative bronchopneumonia, sometimes with pericarditis and pleuritis. Primary, sporadic, fibrinous pneumonia may also occur independent of a connection with mycoplasmal organisms. In both primary and secondary forms, chronic thoracic lesions and polyarthritis may develop.

Pleuropneumonia caused by Actinobacillus pleuropneumoniae (APP), is a severe and highly contagious respiratory disease that can be categorized into peracute, acute, and chronic forms. Pigs in the acute phase have high fevers, and severe dyspnea, and not infrequently, death. The chronic form exhibits as a variable cough with a variety of organ systems impacted (arthritis, pleuritis etc.) Recovered pigs become chronic carriers supporting the worldwide increasing incidence. Vaccination and antibiotic therapy can reduce morbidity, however, the best treatment is prevention through purchase of APP-free pigs.

Swine influenza is an acute respiratory disease resulting from infection with type A influenza virus. One hundred percent morbidity occurs in susceptible herds with animals being markedly ill. Pigs will have high fevers, open-mouthed breathing, nasal discharge and cough. Despite their very ill appearance, swine with uncomplicated infections will recover (mortality < 1%) in about a week’s time. Although this agent can cause infections in humans, it does not occur easily. Humans may also spread the disease to swine. The spread of the disease is attributed to its propagation in young susceptible animals, or in those that have lost a protective titer as well as in those who have recovered but have the ability to still shed the virus for a period of time. Vaccines are licensed for use, but again, the best means of control is to prevent incoming infected swine. Treatment, once infection has occurred, should be aimed at preventing complicating bacterial infections.

Gastrointestinal Diseases

Diarrhea is the hallmark symptom of intestinal diseases with transmission occurring by the fecal-oral route. Often, more than one infectious agent causes the disease. The presence of diarrhea often makes pigs unsuitable for use including those research studies that do not involve the GI system. Age of the animal should be considered when making a list of differential diagnoses. Given that the majority of swine used in biomedical research are adult animals, the focus will be on those agents which impact on adults.

Swine Dysentery, caused by an anaerobic spirochete named Brachyspira hyodysenteriae, occurs mainly in pigs of postweaning age. The disease presents with severe diarrhea with large amounts of mucus and fever. Recovered pigs can continue to shed the organism with carrier pigs and wild rodents being the reservoir for the disease. Supportive fluid therapy and antibiotics are needed to save valuable pigs afflicted with the disease.

Porcine proliferative Enteritis, for which the etiology has been recently identified as the intracellular bacterium Lawsonia intracellularis, primarily afflicts pigs between 6 - 20 wks of age. Infected animals may be asymptomatic, or may, in response to a stressor like shipping, show signs of severe hemorrhagic diarrhea. As the disease progresses, pigs may pass yellow fibrinonecrotic casts that have formed in the ileum. Most affected pigs recover spontaneously, but a significant number develop chronic necrotic enteritis with progressive emaciation. Other animals such as rodents may be a source of infection. Animals can recover and antibiotics can be used to control clinical signs, however, the antibiotic sensitivities of Lawsonia are not well defined.

Salmonellosis in swine is caused by several species with Salmonella cholera suis being the most common. It causes septicemia, cough, dypsnea, pneumonia, cyanosis of the ears and abdomen, fever and diarrhea. S. typhimurium causes a watery diarrhea, fever, anorexia and dehydration. Most pigs recover but some become chronic shedders for several months. It is transmitted by both the fecal-oral route and nasal secretions. Clinical disease should not be treated since recovered pigs can become chronic shedders and because of the zoonotic potential of Salmonella

Transmissible Gastroenteritis (TGE) is a common viral disease of the small intestine that causes vomiting and profuse watery, yellowish diarrhea in pigs of all ages, although it is seen more in nursing and weaning animals. Infection is more common in winter months as viral particles thrive in colder climates. Oral and parenteral administration of vaccine offers the best protection because infection of the intestine elicits a secretory IgA response. Active infection of the intestine with virulent virus provides protective immunity for 6 - 18 months. The best treatment is supportive care with fluids containing glucose and electrolytes.

Reproductive Diseases

Brucellosis is caused by Brucella suis biotypes 1 and 3. It is transmitted by direct contact with contaminated food or water and can enter the body via either the genital or alimentary tracts. Following a bacteremia with seeding of lymph nodes, joints, bone marrow, liver, spleen and genital tract affected swine develop abscesses. Abortion at any stage of gestation, lameness, posterior paralysis and infertility are seen clinically. Abscesses may be found in the testicles, epididymis, uterus, seminal vesicles, intervertebral discs and lymph nodes. A small percentage of animals remain permanently infected and sows can shed the organism for 30 months in vaginal discharges. No treatment has proven effective at eliminating the organism, but some treatments may limit the duration of the bacteremia.

Porcine Parvovirus can remain viable in contaminated secretions and excretions from infected swine for months and is highly resistant to most disinfectants. The organism is shed in semen so acutely infected boars can quickly spread the organisms to a large number of females. Clinical signs include abortion, transient leucopenia, infertility, still born fetuses, neonatal deaths and mummified fetuses. Transplacental infection occurs in the second half of gestation. No treatment has proven to be effective.

Leptospirosis in pigs is caused by several serovars of Leptospira interrogans of which pomona is the most common in herds in the U.S. Infection with L. pomona is usually subclinical as is the acute phase of the disease. A few pigs may show decreased appetite, fever or diarrhea. All leptospirae have an affinity for the kidney where they evade the immune system by localizing in the lumen of proximal tubules. From this location they are shed in the urine and chronically infected animals can shed for 2 years. Animals become infected by breaks in the skin, mucous membranes and conjunctiva. Chronic infection results in abortions, stillborn or weak piglets. Streptomycin, oxytetracycline, erythomycin and tylosin have been shown to be effective at eliminating the pathogen from the renal tubules.

Porcine Reproductive and Respiratory Syndrome (PRRS) is caused by an RNA virus. Clinical signs in infected sows include late term abortions, delayed or premature parturition due to mummified fetuses, fever, pneumonia, and bluish discoloration of the tips of the ear and vulva and subcutaneous edema. Infected piglets may have dypsnea, conjunctivitis, central nervous sytem (CNS) signs, edema of eyelids, blue discoloration of the ears and diarrhea. Antibiotics and supportive therapy have been shown to be effective treatments of piglets.

Glasser’s Disease is caused by Haemophilus parasuis and usually affects pigs from 3 weeks to 4 months of age. Clinical signs include anorexia, depression, lameness, neurologic signs, dypsnea and if chronically infected, chronic arthritis and abortion. It is transmitted via the respiratory tract secretions. Penicillin, cephalosporins, fluoroquinolones, potentiated sulfas, and tylosin are effective treatments.

Erysipelothrix rhusiopathiae serovars 1 and 2 cause most of the clinical disease. Acutely infected swine may not show any signs or they may have rhomboid or diamond shaped pink or purple lesions on the abdomen and back, fever, anorexia, stiff gait, sitting posture, abortion or sudden death. The chronic form is characterized by swollen joints with the hock and carpus most frequently involved and a lameness which is non weight bearing. The organism is harbored in lymphoid tissues and shed in nasal secretions, saliva and feces. Penicillin is the drug of choice, but tylosin and lincomycin also are effective treatments.

Streptococcosis is caused by Streptococcus suis and is transmitted via fomites, direct contact and aerosols. In subclinical carriers the organism is found in the tonsils, reproductive and respiratory tracts. Clinical signs include meningitis, fever, anorexia, pneumonia, convulsions, rhinitis, polyarthritis, vaginitis, abscesses, stillborns endocarditis, myocarditis and death. Antibiotics such as amoxicillin, enrofloxacin, ampicillin and penicillin are effective treatments.

Pseudorabies is caused by a Herpes virus and is transmitted via fomites, direct contact, transplacentally or insemination. The clinical signs vary with the age of pig affected. In adults it results in pneumonia and resorption of fetuses or abortion. Neonatal pigs develop posterior paresis, convulsions, vomiting, diarrhea and CNS signs while older pigs develop pneumonias, coughs and nasal discharges. There is high mortality in neonatal pigs but older ones recover. Vaccination prevents development of clinical signs but does not stop them from viral shedding or infection.

Staphylococcus hyicus gains entrance to the skin via traumatic wounds and is the cause of greasy pig disease. Pigs from 5 days to 2 months old are typically affected. Lethargy, erythematous skin lesions, a crusty lesion which begins in the groin, axilla or behind the ears, erosions of the coronary band; and erosions and ulcers in the mouth, tongue and snout may be seen. Treatment consists of antibiotics which are most effective if given early in the disease.

Swine Pox predominantly affects pigs under 4 months of age. Typical pox lesions consist of reddened macules and papules 1 - 6 mm in diameter which turn to crusted brown to black spots over a period of 3 - 4 weeks. Younger pigs are more severely affected and may have lesions over the body. Transmission of the virus occurs via direct contact with lesions, nasal and oral secretions and the virus may remain viable in dried crusts for up to a year. Treatment consists of supportive care for secondary bacterial infections in the lesions.

Parasitic Diseases

Giardia intestinalis, a zoonotic disease agent located within the small intestine, is commonly present in domestic swine. Its presence may or may not be the primary cause of enteritis. The clinical signs that have been attributed to the parasite include anorexia, depression and loose stools. The cysts are shed in feces intermittently. The afflicted animal responds to treatment with metronidazole. Good husbandry techniques, which include daily sanitization of pens and housing pigs on slatted floors to limit fecal contact, help to control outbreaks.

The swine whipworm, Trichuris suis can cause anorexia, mucoid to hemorrhagic diarrhea and if left untreated can progress to death. Adults are found in the small intestine and cecum. The eggs once passed, take 3 - 4 weeks to develop into the infectious stage. Therefore, as with Giardia, good sanitation and slatted floors control outbreaks. Treatment with anthelmintics mixed into feed is effective in eliminating the infection.

Ascaris suum, the swine ascarid, has the typical direct life cycle of the genus. Following ingestion of embryonated eggs, they hatch and larvae migrate through the liver and lungs. Pathologic lesions may develop as the result of larval migration. The larvae are coughed up, swallowed and return to the small intestine, where they molt into adults. Treatment with anthelmintics and sanitary procedures to prevent exposure to eggs are effective.

Hyostrongilus rubidus, the red stomach worm, has a direct life cycle. After ingestion of eggs, larvae encyst in the gastric mucosa and then return to the stomach lumen. Heavy infestations can cause catarrhal gastritis, poor weight gain and anemia. Treatment with anthelmintics, such as ivermectin, is effective. Good sanitation will break the life cycle.

Trichuris suis, the swine whipworm, has a direct life cycle and colonizes the small intestine and cecum. In young pigs it can cause a profuse bloody diarrhea leading to severe dehydration and death. Steam cleaning is effective in elimination of the eggs but anthelmintic treatment is less effective than for other nematodes. Ivermectin is relatively ineffective and treatment with fenbendazole, dichlorvos or levamisole in the feed may be required.

Trichinella spiralis is rarely encountered as a clinical entity in swine. It may be a zoonotic disease in humans after eating undercooked pork. Most frequently, encysted larvae are observed histologically in muscle tissue with minimal inflammation. Swine are exposed by eating contaminated garbage or carcasses of infected animals. Treatment with albendazole may be effective if required.

Stronglyloides ransomi is found in the small intestine and can infect pigs by the oral, percutaneous, transcolostral and in utero routes. Eggs shed in feces can hatch into infective larvae within 24 hours. Once infected, diarrhea and poor growth can occur. Good husbandry techniques prevent, and antihelmentics cure the infection.

Mange in swine is caused by Sarcoptes scabei var. suis, it is the most significant ectoparasite of swine. Young growing swine develop the acute pruritic form manifested by an intensely pruritic, erythematous dermatitis on the ventral abdomen, trunk and rump. In mature swine thick crusty scabs form on the pinnae and then spread to the neck and head. Ivermectin should be administered orally or subcutaneously in two treatments, 1 to 2 weeks apart.

Lice, Haematopinus suis, cause a pruritic skin lesion along with poor growth and anemia in young pigs. Lice have a predilection for the skin in the flank, neck, axilla and groin. Treatment consists of dusts, sprays, dips, oral or injectable ivermectin.

Non Infectious Diseases

Porcine Stress Syndrome or Malignant Hyperthermia is due to a heritable genetic mutation of the ryr-1 (Hal) gene associated with the calcium-release channel in skeletal muscle. In the research setting it is most likely to be associated with the induction of anesthesia by a wide variety of injectable or inhalant agents, most notably halothane. It may also be encountered in animals under stress, as it is most commonly in agricultural production. The syndrome is characterized by muscular tremors, dyspnea, erythema and hyperthermia. Death may ensue in only a few minutes. Dantrolene 5 mg/kg IV may be used either as a preventative or as a treatment, with supportive therapy. The condition occurs in a wide variety of farm breeds, but has not been reported in miniature pigs. DNA testing can be used as a definitive diagnostic technique, however, it is best to avoid procuring animals from a source known to be affected.

Gastric Ulcers may develop in the pars oesophagea and result in intragastric hemorrhage which may progress from unthrift condition to death. Many management factors may be involved in the etiology, including feed particle size, feed composition, stressful housing situations and stressful protocols. If swine are fed commercially available rations and housed in clean facilities on floors with steady traction, the condition is unlikely to appear in the research setting, unless the protocol itself is stressful. If the condition occurs, it is best to review the management and husbandry techniques as well as the research protocol to determine if the stress factor can be eliminated. The condition may also be treated with antacid agents such as cimetidine.

Neoplasia is uncommon in swine. Malignant melanoma occur in young pigs especially in the Duroc breed and Sinclair miniature pigs, in which the condition has been developed as a genetically reproducible animal model. They primarily appear on the skin and may develop metastases to lymphatic tissues and organs. There is high incidence of spontaneous regression, usually by sexual maturity, and death is uncommon. The most common tumor in swine is the embryonal nephroma.

Pododermatitis, ulcerative dermatitis, callosities and other epidermal lesions are usually associated with trauma or excess moisture in the pen. Solid floors may cause abrasions and contact bedding material, such as wood chips and hay, may accumulate excess moisture which leads to skin lesions if it is not changed with enough frequency. Secondary bacterial infection may occur. Treatment of these conditions is symptomatic, in association with appropriate changes in adverse husbandry factors.

Laboratory Animal Use in Research

Swine have gained prominence as biomedical research models, both as a replacement for other larger animal species and as a model based upon their own anatomic and physiologic characteristics. Textbooks, proceedings books and review articles detail their use in many arenas. Comprehensive descriptions of the use of swine as animal models have been published [1-8,12,14,20-26].

Cardiovascular, digestive and dermal models are the predominant usage of swine in research protocols. The coronary arterial supply is an exacting model for use in the study of myocardial infarction and placement of coronary stents. Swine develop lesions of acute myocardial infarction similar to humans. They develop lesions of atherosclerosis in a manner similar to humans when fed a high fat/high cholesterol diet. The physiology of digestion is similar to humans in spite of the anatomic differences. They are widely used as wound healing models and models of dermal toxicology.

As surgical models, they have been utilized in many types of organ transplantation and are the most likely animal to be used as a source of xenografic organs for humans, if the field becomes clinically feasible.

Training courses in general surgery, laparoscopic surgery and endoscopic procedures extensively use swine. This trend is likely to continue and the number of swine used in research has steadily increased over the last 25 years.

Drug Formulary Table

Species Specific Drug Formulary [1].

Administration of Medications

Intramuscular (IM) and subcutaneous injections (SC) may be given in the neck or rear legs (Fig. 5). In the neck the transition between hairy and hairless skin caudal to the ear has the thinnest fat layer with the muscles close to the skin. The semimembranous, semitendinosus, and gluteal muscles in the rear leg may be used, but may cause more discomfort to the animal than IM injections, given in the neck. A useful method that does not require restraint is to quickly insert a butterfly catheter needle into the side of the neck. Once the animal has recovered from the needle insertion, the handler can inject the medication while the animal walks around the cage.

Figure 5. Intramuscular (IM) and subcutaneous injections (SC) injection sites using a butterfly catheter.

Intravenous sampling or injections sites include the auricular, cephalic, external jugular, cranial vena cava, lateral saphenous and femoral veins (Fig. 6). It is easiest to access these sites in a sedated or anesthetized animal, but they can be acclimated to a sling for sampling from the cranial vena cava. Since most of the peripheral vessels are deep, it is important to know their anatomic location. A 20 gauge 1.5 inch needle is the largest needle necessary for vascular access in swine up to 50 kg. Arterial access is sometimes required for sampling and blood pressure measurements. The most common sites for access are in Figure. 7.

Figure 6. Venous access sites.

Figure 7. Arterial access sites.

Volumes of injections to a given site are related to the size of the animal. IV fluid administration of 5 - 15 ml/kg/hr is appropriate for fluid administration due to dehydration or homeostatic maintenance while under anesthesia. IM injections should be limited to small volumes (1 - 5 ml) of agents that specifically require injection in that site. SC injections may be given in large volumes but generally should not exceed 50 ml/site in the size of pig commonly used in research. Clinical observation of the animal’s reaction to injections should be used as a guide for determining injection volumes.

Several techniques may be used to administer oral medications (Fig. 8). The easiest method is to mix the medication with feed, such as canned dog food or a sweet syrup. Swine usually eat these items readily making it unnecessary to crush or break tablets or capsules. Balling guns, if utilized, should have a flexible neck and swine should be placed in a sling. Stomach tubes may be used if swine are restrained in a sling. The length should be premeasured to reach just caudal to the last rib. The tube should be lubricated, medication quickly administered and the tube removed.

Figure 8. Methods of administering oral medications.

Websites for Swine Suppliers and Informational Databases

Literature databases

Information Resources on Swine in Biomedical Research

Division of Laboratory Animal Resources

USDA APHIS VS CEAH - Swine National Animal Health Monitoring System

Miniature pigs

Sinclair Research Center, Inc.

Ellegaard Göttingen Minipigs

Farm pigs

National Pork Board