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Guinea Pig Husbandry and Medicine
Exotic Pet Medicine
0195-5616/87
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Guinea Pig Husbandry and Medicine
Lynn C. Anderson, D.V.M.*
The guinea pig, or cavy (Cavia porcellus), first become popular as a pet during the 16th century, when Dutch explorers introduced this native South American rodent to European fanciers. Its earliest domestication has been traced to the Andean Indians of Peru, who used guinea pigs as a food source. Guinea pigs were also used as sacrificial offerings to Incan gods. Much of the literature on guinea pig biology and medicine has resulted from their use as research animal models. Since 1780, when Lavoisier used guinea pigs to measure heat production, they have been used in a wide variety of scientific applications. The most notable of these uses include nutrition, toxicology, and immunology. Their large tympanic bullae and classic response to sound have also made guinea pigs particularly useful for auditory research.
ANATOMY Guinea pigs are relatively compact, have virtually no tail, and are taxonomically related to the chinchilla and porcupine. They display a wide variety of coat types and colors. The most commonly seen pets are the shorthaired, smooth-coated English or American varieties, the long, silky-haired Peruvian, and the short, wire-haired Abyssinian. The latter breed may look unhealthy, as its coat is arranged in whorls or rosettes, giving it a ruffled, untidy appearance. Several outbred stocks and inbred strains 2 and 13 have been developed primarily for research purposes. A hairless guinea pig has been recently developed for research in transdermal drug penetration and other studies in which hair may interfere with research efforts. Various coat colors, including white, red, tan, brown, chocolate, and black, may be exhibited singly in monochromatic animals or as bands or patches in bicolored or tricolored specimens. · ' In a healthy guinea pig, the hair has a low luster. Tactile hairs are arranged in five to six rows on the muzzle, with two pairs around the eye. The triangular oral opening is small, making inspection of the oral cavity *Diplomate, American College of Laboratory Animal Medicine; Manager, Veterinary Research , Amgen Inc. , Thousand Oaks, California
Veterinary Clinics of North America: Small Animal Practice-Vol. 17, JI.Jo. 5, September 1987
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Figure 1. Male (boar) genitalia showing digital extrusion of the penis. The scrotal sacs, which are separated by the anal opening, lie below the penis.
difficult without sedation or anesthesia. Guinea pigs are monogastric herbivores. They have hypsodontic (open-rooted and continuously erupting) teeth, with the pattern of 1/1 incisors, 111 premolars, and 3/3 molars. In the absence of canine teeth, there is a diastema between the chisel-like incisors and the flat premolars and molars. The latter teeth are used for grinding; consequently, the masticatory muscles are well developed. Other distinguishing external features include the forefeet, which have four toes each, and the hindfeet, which have three toes each. Both male and female guinea pigs have one pair of inguinal nipples, although only the female has mammary glands. The male's penis is normally retracted and opens slightly ventral to the anus. Sex identification may be accomplished by palpating the penis or testes or by gently retracting the preputial skin to extrude the penis (Fig. 1). The female normally has an intact vaginal closure membrane, which lies in a shallow U-shaped fold between the anus and urethral opening (Fig. 2). During estrus and parturition, this membrane is perforated. Postmortem examination of a normal, healthy guinea pig reveals several characteristics of comparative interest. Unlike stomachs in other rodents, the guinea pig's stomach is nonglandular, and the closely associated spleen is relatively broad. Females have significantly larger and heavier spleens than males. As is typical of herbivores, much of the digestive process occurs in the cecum, which may contain up to 65 per cent of the gastrointestinal
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orifice Vaginal orifice
Figure 2. Female (sow) genitalia showing the urethral orifice, the vaginal orifice (covered by a membrane), and the anal opening.
contents. The adrenal glands are relatively large, bilobed, and triangular. The inguinal canals, which contain the testes, remain open throughout life. The male's coiled, tubular vesicular glands lie ventral to the ureters and extend approximately lO em into the abdominal cavity from their base in the pubic area. These glands should not be confused with the female's bicornate uterine horns.
BEHAVIOR The docile temperament and lack of objectional odor of guinea pigs enhance their acceptability as pets. They seldom bite or scratch if handled frequently and gently. When startled by a loud noise, sudden movement, or strange environment, guinea pigs may freeze and maintain position for up to 20 minutes or scatter and leap. Guinea pigs vocalize when frightened by making a series of short calls (chutters), whining, or whistling. When frightened, guinea pigs scatter their bedding and food, push ingesta into sipper tubes, and foul food and >Vater. Groups of guinea pigs establish a social hierarchy with one dominant (alpha) male. Animals of lower rank may develop hair loss from fur chewing (barbering) by the more dominant members. Young animals may pull hair
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from their dams. However, pregnant sows often lose hair during the later stages of gestation, and weaning guinea pigs may develop thin hair as their neonatal fur drops out and is gradually replaced by mature hair. The sick guinea pig commonly is immobile and has dull, moist eyes and a nasal discharge. REPRODUCTION
For successful breeding programs, guinea pigs may be housed in pairs or harems of 4 to 10 females per male. Females should first be bred between 3 and 7 months of age. After 7 months, the pelvic symphysis may be permanently fused; parturition may be complicated by dystocia and, ultimately, maternal and fetal deaths. The first estrus is significantly less fertile than subsequent matings. Although males may display sexual behavior as early as 30 days of age, fertile matings will not be achieved until 3 to 4 months of age or at 550 to 600 gm body weight for males and 350 to 450 gm body weight for females. Spontaneous ovulation occurs approximately 10 hours after the onset of estrus, which is characterized by perforation of the vaginal membrane. This membrane reforms after ovulation. The normal estrous cycle is 16 days, and estrus lasts an average of 8 hours. A fertile postpartum estrus occurs 6 to 15 hours after parturition. Artificial insemination has been used successfully in guinea pigs. Ideally, the semen should be deposited at the onset of estrus because late fertilization will result in increased numbers of abortions, stillbirths, or decreased litter size. The guinea pig has an unusually long gestation compared with other rodents. The length of pregnancy will vary from 58 to 72 days and is inversely related to litter size. Fetuses may be palpated as early as 15 days postconception. During late pregnancy, the sow's abdomen will be grossly distended, and she may double in weight. The prominent sign of impending parturition is the separation of the pubic symphysis during the last week of pregnancy. The separation increases to 3 em during the final prepartum hours. Because gestation length is variable and no nests are built, the onset of parturition is unpredictable. Delivery of the young normally takes 30 minutes, with 3 to 7 minutes between pups. Dystocias may occur in sows bred for the first time after 7 months or if fetuses are large. Dystocia should be suspected if the sow becomes depressed or produces a greenish-brown vaginal discharge. Digital manipulation of the neonate or caesarean section may be performed. , The relatively long period of in utero development produces young that are nearly self-sufficient and weigh 60 to 100 gm at birth. Young weighing 50 gm or less rarely survive. Newborns are ambulatory, fully furred, and have erupted teeth and open eyes. Despite the presence of only two nipples, a sow may successfully raise five or six offspring. The young may begin to eat solids and drink water from a bowl within several hours of birth, but they should continue to nurse for 14 to 21 days.or until they weigh 180 gm. If necessary, hand rearing of neonates over 60 gm is possible, but hand
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rearing should not begin until12 to 24 hours postparturition. Fortified guinea pig food, softened with milk or water, may be used for this purpose, but it may not sustain normal growth. Lactating sows will readily nurse offspring from another litter, and older young will strip all sows in a colony. Young should nurse at least 15 days, but they begin eating solid food at 2 to 3 days.
MAINTENANCE
Guinea pigs are often presented with nonspecific complaints of decreased alertness and activity, depressed appetite, or weight loss. The case history should include a thorough review of the animal's normal habitat and diet and the owner's husbandry practices because many diseases are the consequence of improper maintenance. Antibiotic therapy is often contraindicated because it may induce lethal effects. Therefore, preventive measures are critical to the animal's survival. Anorexia, a common nonspecific sign in guinea pigs, is treated with force-fed meals of a slurry of yogurt, guinea pig food, vitamin C, ground guinea pig fecal pellets, and treatment for the specific malady. In the wild, guinea pigs live in open, grassy habitats or burrows that were excavated, then deserted, by other animals. The group normally feeds and rests together at time intervals based on day length and ambient temperature. Cage Design Domestic guinea pigs are hardy, inexpensive, and fairly easy to maintain in mixed groups, pairs, or as individuals. In general, their habitat should be easy to clean and should protect the animals from injury or drafts. The cage or pen should provide adequate floor space, which is estimated per animal at 101 square inches for adults or 180 square inches for breeders. Overcrowding is associated with decreased reproduction and increased hair chewing. The walls of an enclosed cage should be at least 7 inches high. The sides of an open pen should be 10 inches high to prevent the animals, especially males, from escaping. The habitat may be constructed from solid plastic or stainless steel slats or wire mesh. Wood should be avoided because it is difficult to clean, and galvanized metal tends to rust and corrode. When wire mesh is used for flooring, it should form %-inch squares or 0.5- X 3.0-inch rectangles to provide adequate footing. Some breeders prefer wire mesh b<:;cause it allows urine and fecal pellets to drop through, thus protecting the animals from contact with wet, soiled bedding. However, wire mesh has been associated with hair loss, footpad ulcers, and decreased breeding and weight gain. Young guinea pigs raised in solid-bottom cages do not adapt well to mesh and may develop severe foot injuries or fractured legs. Solid-bottom cages with bedding provide more warmth and protection. Wood shavings or shredded paper are preferable to sawdust, which may form _an impaction around the penis and inhibit copulation.
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Temperature and Humidity Guinea pigs do well in a stable environment in which the temperature is maintained at a constant level ( ± 2°F) within a range of 65 to 75°F (18 to 24°C). Their compact size allows them to tolerate cold more readily than high ambient temperatures. The room humidity may be maintained between 40 per cent and 70 per cent, although 50 per cent is considered ideal. Both the temperature and humidity within a cage may vary considerably from room values, depending on the construction and bedding materials, number of animals, level of sanitation, and ventilation rate. High temperatures may interfere with reproduction, and cool, moist environments may predispose the animals to respiratory infections. Sanitation Frequency of sanitization will depend on housing construction and animal population per unit. Solid-bottom cages must be cleaned more often than those with wire mesh or slatted floors, which allow urine and feces to pass through into collecting pans. In general, cages should be cleaned and sanitized once a week. Water containers and feeders may require more frequent cleaning, especially if the animals urinate and defecate in them. Guinea pigs also tend to contaminate water bottles by chewing on the sipper tubes and clogging them with food particles. Sanitation may be accomplished with a hypochlorite solution or detergent; a vinegar or other weak acid solution will aid in removing scale deposited by crystalline urine. Regardless of the products used, the cages should be thoroughly rinsed with clean water. If bedding is used, the cages should first be dried, and the depth of bedding should not extend to the level of the sipper tube or it will act as a wick and drain the bottle.
NUTRITION
In their native habitats, guinea pigs feed on grasses, roots, fruits, and seeds. The dietary requirements for laboratory guinea pigs have been established by the National Academy of Sciences and may be adapted for pet animals. Guinea pigs do not adapt well to changes in diet or readily accept salty, bitter, or sweet rations. Complete, highly palatable diets containing 18 per cent to 20 per cent protein, 4 per cent fat, and 16 per cent fiber produced the highest level of nonspecific immunity factors in one study. Many of the required vitamins are produced by the intestinal microflora. The role of coprophagy in nutrition is unclear, but pr,evention of fecal ingestion has caused weight loss and altered mineral excretion. Unlike most mammals, guinea pigs require a high level of folic acid. Like primates, they are also dependent on a dietary source of vitamin C because of an absence of L-gulonolactone oxidase. Approximately 800 to 1500 mg of vitamin C are added per kilogram of fortified rations. Despite appropriate food storage in a cool, dry area, vitamin C is degraded to approximately 50 per cent of the postprocessing levels within 6 weeks. Deterioration in water, especially in dirty and lighted containers, occurs in
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Table I.
General and Reproductive Data'a.zt.2:3.30.35.38
Adult body weight Male Female Life span Average Maximum Rectal temperature
900-1200 gm 700-900 gm 3-4 yr 6-7 yr 37.9-39.5°C 100.2-103.1°F 90-150/min 230-320/min
Respiration rate Heart rate Blood volume
69-75 ml/kg body wt (4.5-8.3% BW)
Reproductive data First estrus (average) First breeding Male Female Estrous cycle Estrous length Gestation Litter size Average Maximum Breeding life span
68 d 600--700 gm (3-4 mo) 350-450 gm (2-3 mo) 15-17 d 8.2 hr 58-72 d (average, 68 d) 3-4 6-7 18-20 mo
hours or a few days . Fortified diets over 90 days since milling, or those containing less than 200 mg of vitamin C per kilogram diet, should be discarded or supplemented with 10 mg of vitamin C per kilogram body weight per day (20 mg per kg per day for pregnant or lactating animals). This may be accomplished by feeding a handful of fresh , cleaned kale or cabbage on a daily basis. Alternatively, 200 mg of ascorbic acid may be added to each liter of drinking water. These levels are based on an average food consumption of 6 gm per 100 gm body weight per day and water consumption of 10 ml per 100 gm body weight per day. The practice of supplementing fortified pelleted diets with hay or greens is controversial. Productivity may be improved when hay is provided. In one study, neonatal deaths and postweaning culls were reduced after greens were eliminated. Others have claimed that hay helps prevent overgrown teeth and behavior problems such as barbering. Dirty hay or moldy fruit and vegetable supplements are potential sources of microbial pathogens.
PHYSIOLOGY As in other species, the guinea pig's genetics, age, reproductive status, microflora, environment, and diet will influence its physiologic parameters. Many reference texts provide normal data or, more appropriately, "approximate values," which are summarized in Table 1. The si-te and techniques used for blood collection, as well as the methodology and instrumentation
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employed for analysis, will also affect hematology and serum chemistry values . Small blood samples are most readily collected by clipping a toenail or from the retro-orbital sinus. It is more difficult to collect larger samples from the femoral artery or vein. Cardiac puncture is impractical in clinical situations because of the high degree of risk involved. The erythrocyte count increases with age, whereas the reticulocyte count decreases. The erythrocytes are less fragile than those in dogs, but more fragile than those in cats or ruminants. The most prevalent leukocytes are lymphocytes. Neutrophils contain red granules in the cytoplasm. The differential evaluation should include a unique mononuclear cell, known as the Kurloff cell. This cell, characterized by its large mucopolysaccharide eosinophilic intracytoplasmic inclusion body, originates primarily in the spleen. It is commonly classified as a leukocyte and is thought to offer fetal protection from sensitized lymphocytes and IgM molecules. Both endogenous and exogenous estrogen will increase the number of Kurloff cells in the peripheral blood. CLINICAL EXAMINATION AND RESTRAINT The initial clinical examination should be conducted in a quiet room, taking care not to make sudden movements or loud noises that will elicit the characteristic freeze or scatter response. The animal should be placed in a box or cage and observed for coat condition, stance, and attitude. Physical examination requires minimal restraint. The animal should be lifted from its container by grasping it gently under the thorax with one hand and supporting the hindquarters with the opposite hand. Lung and liver injuries and diaphragmatic hernias have been associated with excessive pressure around the abdomen and thorax. The chest is easily auscultated, and the abdomen may be gently palpated. A lighted otoscopic speculum or tube is useful for examining the oral cavity of a sedated guinea pig. DISEASES The guinea pig is susceptible to a number of naturally occurring and experimentally induced diseases. Only those of clinical significance are reviewed in the following section. Bacterial Diseases
Integumentary. Cervical lymphadenitis or "lumps",is most frequently caused by Streptococcus zooepidemicus, although Streptobacillus moniliformis has been rarely isolated from cervical abscesses. Streptococcus zooepidemicus may also cause generalized abscesses, septicemia, uterine infections, panophthalmitis, and otitis media. Transmission most likely occurs via oral lesions caused by coarse food , such as hay , or skin abrasions from fighting, or in an improperly maintained environment. Aerosol infections have been induced experimentally. Fluctuant subcutaneous masses noted in the ventral cervical region involve primarily the submaxillary lymph nodes
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and may interfere with deglutition. Abscesses may rupture spontaneously, exuding a thick, creamy yellowish-white pus. Microscopic examination of this material, collected from the peripheral surface, should reveal chains of gram-positive cocci. Antibiotic therapy will be ineffective if the abscesses are well encapsulated. Surgical drainage and abscess removal may be successful, but intervention may produce septicemia, causing suppuration and abscessation in many organs. Pododermatitis, caused by Staphylococcus aureus, is another clinical problem associated with poor environmental conditions, particularly fecal contamination of wire-bottom cages. This condition is most often seen on the forefeet of obese animals. Firm, ulcerated masses up to 3 em in diameter develop on the feet, causing the animals to shift weight and become relatively inactive. Chronic infections may lead to osteoarthritis and amyloidosis of the kidney, liver, spleen, and adrenal glands. Local or systemic antibiotic therapy or bandaging may help, but the habitat must be clean and smooth. Staphylococcus aureus was isolated from a group of guinea pigs with erythematous skin on the ventral abdomen and thorax, followed by exfoliation of the epidermis. Most of these cases occurred in pregnant animals. Respiratory. Pneumonia is one of the most common bacterial diseases of guinea pigs. Bordetella bronchiseptica, Streptococcus pneumoniae, and Klebsiella pneumoniae may be cultured from the respiratory tract of asymptomatic guinea pigs, but under suboptimal conditions, nutritional deficiencies, inadequate ventilation, high humidity, and temperature extremes, the animal is predisposed to diseases caused by these organisms. Animals may die without premonitory signs. In advanced, chronic cases, breathing is labored due to bronchopneumonia and lung consolidation. Purulent nasal discharge is usually associated with Klebsiella infection. Bordetella bronchiseptica and pneumococcal infections may also cause conjunctivitis, otitis media, stillbirths, and abortions. Culture and identification are required for definitive diagnosis of the causative agent. Treatment of sensitive strains with antibiotics may control the disease but will not eliminate the carrier state. Antibiotic therapy may also produce a variety of toxic signs, which are detailed later in this article. A killed bacterin has been used to eliminate B. bronchiseptica from one large research breeding colony, and Tribrissen given at 10 mg per kg subcutaneously (SQ) has been used successfully for treating pneumonia. The prognosis remains poor. Protection against this bacterial infection has been accomplished with an intranasal vaccination, using a temperature-sensitive mutant. Rats and rabbits may harbor B. bronchiseptica in their respiratory tracts; therefore, these animals should not be housed with guinea pigs. Pasteurella, Actinobacillus, and Pseudomonas aeruginosa have been infrequently associated with pneumonia of guinea pigs. Auditory. Otitis media is frequently associated with respiratory infections, but it is often clinically inapparent. A retrospective survey of 1373 guinea pig necropsies at one institution indicated a 13 per cent incidence of otitis media. The bacteria most commonly isolated were Streptococcus pneumoniae (20 per cent), S. zooepidemicus (15 per cent), B. bronchiseptica (12 per cent), and P. aeruginosa (II per cent). Radiology of the tympanic bullae was 96 per cent accurate and superior to otoscopy for diagnosis. Extension into the inner ear may produce torticollis, ataxia, rolling, or circling.
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Gastrointestinal. Enteric Salmonella infections are most commonly caused by S. typhimurium or S. enterititis, which are introduced through fecal contamination of green vegetables and water. These organisms may produce an acute, fatal septicemia. Animals often die without clinical signs or following nonspecific signs of lethargy and emaciation. Diarrhea is uncommon. Postmortem lesions may be absent in acute cases. Splenomegaly, lymphadenopathy, and liver and spleen necrosis are seen in subacute and chronic cases. Granulomas may also be evident in liver, spleen, lungs, small intestine, and uterus. Fecal culture may be useful antemortem; postmortem isolation from the spleen is more reliable. Antibiotic therapy may stop an epizootic, but will not eliminate carriers. In a colony situation, it is best to depopulate and disinfect, although a mass fecal monitoring program was used successfully to eliminate the disease in a valuable research colony. Bacillus piliformis, Campylobacter, Escherichia coli, and Yesinia pseudotuberculosis have been infrequently associated with enteric disease characterized by wasting and diarrhea. Reproductive. Bacterial mastitis is often a fatal disease caused by E. coli or, less frequently, Klebsiella, S. zooepidemicus, or Proteus. In the male, preputial dermatitis results from trauma, followed by swelling and ulceration of the prepuce and perineum. In one case report, unidentified bacterial colonies were detected by histologic examination of these areas. Treatment with thorough daily cleaning and application of zinc-oxide ointment to the perineal area has been successful. Viral Diseases
Most viral infections of guinea pigs are mild or inapparent. These diseases are seldom of clinical significance, but they may serve as valuable models of human disease, or they may complicate unrelated research projects. Spontaneous, transplantable lymphatic leukemia has been reported in guinea pigs with moderate to marked lymphocytosis, lymphadenopathy, splenomegaly, and hepatomegaly. Hindlimb paralysis and progressive flaccid paralysis have been observed in animals with polio virus and lymphocytic choriomeningitis infections, respectively. In one colony, an epizootic oflethal pneumonia was attributed to an adenovirus. A mild, transient conjunctivitis of juvenile guinea pigs is caused by a chlamydia. This agent produces characteristic cytoplasmic inclusions in conjunctival epithelial cells. Mycotic Diseases Most mycotic infections are dermatophytoses caused by Trichophyton mentagrophytes. Young animals are generally more susceptible than adults. Guinea pigs may be asymptomatic carriers or have areas of patchy alopecia on the face, nose, and ears. These areas may extend along the dorsal trunk and develop into hyperkeratotic lesions with vesicles around the periphery. This organism will not fluoresce under ultraviolet light. Provisional diagnosis is accomplished by microscopic examination of keratinized epithelial cells or affected hair surfaces and identification of arthospores and hyphae. Cultures should be held a minimum of 3 weeks fot: definitive diagnosis. Successful treatment with topical or systemic griseofulvin therapy has been reported, although high infant mortality was associated with oral adminis-
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tration in one colony. Orally administered tolcidate and tolnaftate were effective in a controlled study. Moldy hay has been incriminated as the source of phycornycoses in young guinea pigs. Candida albicans is present in the normal gastrointestinal flora and may cause mild, transient conjunctivitis in young guinea pigs. Endoparasites Few clinical symptoms are associated with endoparasites. A large variety of protozoa normally inhabit the cecum and colon, and complications due to these organisms are generally associated with either poor husbandry or severe debilitation from other causes. Coccidiosis caused by Eimeria caviae may cause weakness, ~maciation, and severe diarrhea, but the disease normally responds to sulfonamide therapy. Cryptosporidia rarely cause diarrhea. Serologic surveys suggest that Toxoplasma gondii infection is more prevalent than pathologic evidence of infection would indicate. Klosiella cobayae are occasionally detected on postmortem histologic examination of the kidneys, but these coccidia cause no clinical signs. Renal and brain lesions have been infrequently reported in guinea pigs infected with Encephalitozoan. Housing guinea pigs with Encephalitozoan-infected rabbits should be avoided. Paraspidodera uncinata is a short (11 to 28 mm) nematode that may be found in the cecum but is not usually pathogenic. Injectable levamisole has been used successfully to control this pinworm infection. Experimental and natural infections with the trematode Fascioloides have also been reported. Eetoparasites Lice are easily detected upon close examination of the fur, where both adults and eggs attach to the hair shaft. Gliricola porcelli is more common than Gyropus ovalis, the latter having a smaller, less rounded head than the former. The mouth parts are used to abrade the skin and harvest cutaneous fluids. The mid- and hindlegs of these lice bear tarsi with only one or no claws. Heavy infestations cause alopecia and pruritis, and infestations may be effectively treated with lindane or malathion dusts. A sarcoptid mite, Trixacarus caviae, has been reported in pet guinea pigs with mixed clinical histories. In one instance, the guinea pigs had hyperkeratotic skin, with or without alopecia, and no pruritis. All areas of the body, except the lower limbs, were affected. In another report, the guinea pig displayed intense pruritis, characterized by self-inflicted wounds and furious running and circling. Identification of the mite may require repeated skin scrapings miXed with 10 per cent potassium hydrpxide. Treatment may be accomplished with shampooing, followed by exposure to dichlorvos strips 1 day a week for 6 weeks, diluted 1:40 lime-sulfur baths, or once weekly applications of 10 per cent lindane for 3 weeks. lvermectin injectable at 200 mg per kg SQ is a useful treatment for ectoparasitism. Heavy infestations of the mite Chirodiscoides caviae may also cause pruritis and alopecia, but it is generally considered to be harmless. Other mites have been rarely identified in guinea pigs, includil)g Demodex caviae, Sarcoptes scabei, and Notoedres muris.
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Nutritional and Metabolic Disorders Guinea pigs have been used as a model for many nutritional studies; however, only those of clinical significance are included in this article. The guinea pig's dependence on exogenous vitamin C and the vitamin's labile characteristics make these animals particularly susceptible to scurvy. Clinical symptoms of scorbutus include inappetance, diarrhea, reluctance to move, swollen, painful joints, impaired or deformed bone and teeth formation, gingival, costochondral, and muscle hemorrhages, and delayed wound healing. Secondary infections are common and presumably are the result of depressed phagocytic activity caused by vitamin C deficiency. Response to treatment is dramatic, provided that the animals are given sufficient daily quantities (25 mg per kg) of the vitamin until recovery and until the predisposing factors are corrected. Widespread metastatic calcification of soft tissues may cause lameness, or they may be found incidentally on postmortem examination. This condition is secondary to an alteration in the complex relationship among calcium, phosphorus, magnesium, and potassium. Experimental diets high in cholesterol have caused hemolytic anemia. Malocclusion of premolar teeth causes a syndrome commonly known as slobbers. Animals are inappetant, lose weight, and have moist skin around the mouth, chin, and ventral neck. The mandibular molars are overgrown in the lingual direction, and the maxillary molars are excessively worn. Subacute scurvy and chronic fluorosis may cause similar clinical signs and should always be considered. Spontaneous, contagious diabetes mellitus has been reported in one colony. These animals have elevated glucose-tolerance test values and glycosuria. Pregnancy toxemia is most often seen during the first or second gestation of obese, stressed guinea pigs. Clinical signs develop 7 to 10 days prior to parturition and may include nonspecific signs such as lethargy and anorexia. Blood glucose is markedly decreased, and urine pH is acidic and contains protein. Rapid mobilization of lipids leads to ketosis, coma, and death. The primary cause may be inadequate blood flow through uterine arteries. Antibiotic Toxicity From a clinical standpoint, the guinea pig's marked, often lethal sensitivity to antibiotic therapy cannot be overemphasized. The predominant gastrointestinal microflora are usually gram-positive anaerobic cocci and lactobacilli. Escherichia coli are normally absent or present in small numbers, as are Clostridia. Antibiotics alter the normal microflora and may cause an enterotoxemia and consequent clinical signs. Agents that have been reported to cause enterotoxemia include penicillin, ampicillin, bacitracin, erythromycin, spiramycin, streptomycin, lincomycin, gentamicin, clindamycin, vancomycin, and (variably) tetracycline. As little as 50,000 units of penicillin given intramuscularly (IM) will cause 20 to 100 per cent mortality within 3 to 5 days. Topical antibiotics have also produced the lethal syndrome. The animals appear normal for 24 to 48 hours, tnen become active, anorexic, and hypothermic. Some may have diarrhea. By 72 hours, the gait is unsteady,
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Table 2.
Therapeutic Drug Dosages ANTIMICROBJALS7• 18•23
Agent
Dose
Route
Sulfamethazine
PO
Chloramphenicol sodium succinate
1 mg/ml drinking water up to 60 days 12.5 mg/kg, once a day for 5-14 days 5 mg/kg, twice a day for 4 days, may repeat after 4 days withdrawal 30 mg kg, twice a day for 5 days
Agent
Dose
Route
Indications
Sulfamethazine
1 gm/L drinking water for 5 days 0.25 gm/L drinking water for 30 days 25 mg!kg, once only 0.1% spray, 5% dust 1% dip, once a week for 3 weeks 1:40 dilution with H,O, bath
PO
Coccidia
PO
C ryptosporidium
SQ Topical Topical
Parasidodera
Topical
Mites
Cephaloridine Oxytetracycline
IM 1M
IM
ANTHELMINTICS 10• 18•30•42 •43
Sulfaquinoxaline Levamisole Malathion Lindane Lime-sulfur
Lice Mites
OTHER37
Agent
Dose
Route
Indications
Griseofulvin
15 mg!kg once a day for 14-28 days
PO
Trichophyton
respiration increases, and the animals become prostrate shortly before death. The most common postmortem lesions are colitis and a distended, fluid- and gas-filled cecum. A less frequently seen hemorrhagic syndrome has been reported in animals that suddenly die with visceral hemorrhages, leukopenia, and thrombocytopenia. Chronically administered, low doses of antibiotics may cause stunted growth, alopecia, and neurologic signs. The pathogenesis of antibiotic toxicity is not fully understood, but it is associated with an increase in the number of coliforms and anaerobic rods (Clostridium), along with a decrease in anaerobic gram-positive organisms. Toxicity may be caused by absorption of E. coli-produced endotoxin or clostridial enterotoxins. Systemically administered chloramphenicol, cephaloridine, low doses of sulfonamides, topical neomycin, and polymixin B have been used successfully to counter lethal antibiotic effects. Parenteral tetracycline used for 3 to 4 days or on alternate 4-day periods may be tolerated for therapy of infectious disease. Suggested drug dosages are listed in Table 2.
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NEOPLASIA Most neoplasms are found incidentally on postmortem examination. In one survey, nearly one third of all tumors were found in the respiratory tract. The neoplasms most likely to be encountered clinically are the benign skin tumor trichofolliculoma or leukemia. ANESTHESIA AND EUTHANASIA Sedation or anesthesia may be required to facilitate physical examination, radiography, or sample collection. The most common surgical procedures are superficial skin incisions or excisions, caesarean sections, and castrations. The recommended dosages are described in the article "Anesthesia and Surgery of Laboratory Animals," but responses are extremely variable. Self-mutilation of distal limbs has been associated with parenteral administration of lnnovar-Vet and ketamine hydrochloride. Furthermore, ketamine provides poor analgesia and muscle relaxation. Ether causes marked salivation and is flammable. Although the use of ether is discouraged, if it is used, it should be preceded by atropine sulfate administration. Methoxyflurane is the inhalant anesthetic of choice. Euthanasia may be accomplished by administering overdoses of barbiturates or by giving one of the commercially available injectable euthanasia agents intraperito~eally. PUBLIC HEALTH SIGNIFICANCE A number of organisms that infect or inhabit guinea pigs are potentially zoonotic, but these organisms are seldom associated with human disease. These organisms include Salmonella, Campylobacter, lymphocytic choriomeningitis, and Sarcoptes. Allergy to gqinea pig dander is most frequently reported in personnel who have frequent contact with the animals, such as laboratory technicians. Clinical symptoms in human beings include rhinitis, asthma, and skin rashes. Skin tests are not always reliable indicators of sensitivity, but they may be useful in some instances because false positives are rare. ACKNOWLEDGMENTS
The author gratefully acknowledges the assistance of the secretarial and librl!ry staffs and the general support of the Amgen Corporation in the preparation of this article.
REFERENCES 1. Balsari A, Bianchi C, Cocilovo A, et al: Dermatophytes in clinically healthy laboratory animals. Lab Anim 15:75-78, 1981
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2. Bett NJ, Hynd JW, Green CJ: Successful anaesthesia and small-bowel anastomosis in the guinea pig. Lab Anim 14:225-228, 1980 3. Boot R, Oosterom J, Walvoort HC: Recovery of members of the Pasteurella-Actinobacillus group from guinea pigs. Lab Anim 17:285-289, 1983 4. Breazile JE, Brown EM: Anatomy. In Wagner JE, Manning PJ (eds): The Biology of the Guinea Pig. New York, Academic Press, 1976, pp 53-62 5. Clarke HE, Coates ME, Eva KJ, et al: Dietary standards for laboratory animals: Report of the Laboratory Animals Centre Diets Advisory Committee. Lab Anim 11:1-28, 1977 6. Crockcroft A, McCarthy P, Edwards J, eta!: Allergy in laboratory animal workers. Lancet 1:827-830, 1981 7. Dixon LW: Antibiotic toxicosis in the guinea pig. Texas Vet Med J 48:31, 1986 8. Doyle RE , Sharp GC , Irvin WS , et a!: Reproductive performance and fertility testing in strain 13 and Harley guinea pigs. Lab Anim Sci 26:573-580, 1976 9. Ediger RD: Care and management. In Wagner JE, Manning PJ (eds): The Biology of the Guinea Pig. New York, Academic Press 1976, pp 5-12 10. Eliazian M, Shahlapour A, Tamiji Y: Control of Paraspidodera uncinata in guinea pigs with levamisole. Lab Anim 9:381-382, 1975 11. Eva JK, Fifield R, Rickett M: Decomposition of supplementary vitamin C in diets compounded for laboratory animals. Lab Anim 10:157-159, 1976 12. Eveleigh JR: The breeding performance of the Pirbright Dunkin Hartley guinea pig after discontinuing the feeding of green food as a supplement with particular reference to productivity. Lab Anim 14:55-58, 1980 13. Feuerman E, Alteras I , Honig E, et al: Saprophytic occurrence of Trichophyton mentagrophytes and Microsporum gypseum in the coats of healthy laboratory animals. Mycopathologia 55:13-16, 1975 14. Foreyt WJ: Fascioloides magna development in selected nonruminant mammalian hosts. Exp Parasitol 47:292-296, 1979 15. Ganaway JR, Allen AM : Obesity predisposes to pregnancy toxemia (ketosis) of guinea pigs. Lab Anim Sci 21 :40-44, 1971 16. Gannon J: A Survey of Encephalitozoon cuniculi in laboratory animal colonies in the UK. Lab Anim 14:91-94, 1980 17. Green CJ: Neuroleptanalgesic drug combinations in the anesthetic management of small laboratory animals. Lab Anim 9:161-178, 1978 18. Harkness JE, Wagner JE: The Biology and Medicine of Rabbits and Rodents. Edition 2. Philadelphia, Lea & Febiger, 1983 19. Harper LV: Behavior. In Wagner JE, Manning PJ (eds): The Biology of the Guinea Pig. New York, Academic Press, 1976, pp 31-51 20. Hill BF: The guinea pig: Management and research use. In Charles River Digest. Volume 9. Wilmington, Massachusetts, The Charles River Breeding Laboratories, Inc., 1972, p 1 21. Hill BF: The guinea pig: Management and research use. II. In Charles River Digest. Volume 19. Wilmington, Massachusetts, The Charles River Breeding Laboratories, Inc., 1980, pp 1-4 22. Hochman D, Blanchard J: Simplified method for intravenous dosing and serial blood sampling of unanesthetized guinea pigs. J Pharm Sci 72:975-976, 1983 23. Holmes DO: Clinical Laboratory Animal Medicine: An Introduction. Ames, The Iowa State University Press, 1984 24. Hughes HD Jr: Anesthesia of laboratory animals. Lab Anim 10:40-56, 1981 25. Ishihara C: An exfoliative skin disease in guinea pigs due to Staphylococcus aureus. Lab Anim Sci 30:552-557, 1980 26. Kinkier RJ Jr., Wagner JE, Doyle RE , et al: Bacterial mastitis in guinea pigs. Lab Anim Sci 26:214-217, 1976 27. Lebengarts YZ, Rybakova, AM, Orlova AV: The effect of different diets on some indices of nonspecific immunological reactivity of guinea pigs. Vopr Pi tan 3:63-66, 1977 28. Lee KJ, Johnson WD , Lang CM: Preputial dermatitis in male guinea pigs. Lab Anim Sci 28:99, 1978 29. Manning PJ: Neoplastic diseases. In Wagner JE , Manning PJ (eds). The Biology of the Guinea Pig. New York, Academic Press, 1976, pp 211-225 • 30. Manning PJ, Wagner JE, Harkness JE: Biology and diseases of guinea pigs. In Fox JG,
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Cohen BJ, Loew FM (eds): Laboratory Animal Medicine. Orlando, Academic Press, 1984, pp 149-181 McLean AJ, Boquest A: Enteric flora of normal laboratory guinea pigs. Br J Exp Pathol 58:251-254, 1977 Newton WM, Cusick PK, Raffe MR: Innovar-vet induced pathologic changes in the guinea pig. Lab Anim Sci 25:597-601, 1975 Olfert ED, Ward GE, Stevenson D: Salmonella typhimurium infection in guinea pigs, observations on monitoring and control. Lab Anim Sci 26:78-80, 1976 Orlovski VI, Bochkov lA, EmeJ'yanenko IN: The effect of antibiotics on the microflora of the guinea pig intestinal tract. Antibiotiki 20:902-903, 1975 Phoenix CH: Guinea pigs. In Hafez ESE (ed): Reproduction and Breeding Techniques for Laboratory Animals. Philadelphia, Lea & Febiger, 1970, pp 244-257 Pombier EC, Kim JCS: An epizootic outbreak of ringworm in a guinea pig colony caused by Trichophyton mentagrophytes. Lab Anim 9:215-221 , 1975 Reid, ME, Bieri JG: Nutrient requirements of the guinea pig. In Nutrient Requirements of Laboratory Animals. Washington, DC, National Academy of Sciences, 1978 Sisk DC: Physiology. In Wagner JE , Manning PJ (eds): The Biology of the Guinea Pig. New York, Academic Press, 1976, pp 63-98 Wagner JE: Introduction and taxonomy. In Wagner JE , Manning PJ (eds): The Biology of the Guinea Pig. New York, Academic Press, 1976, pp 1-4 Wagner JE, Owens DR, Kusewitt DF, et al: Otitis media of guinea pigs. Lab Anim Sci 26:902-907, 1976 Weber J, Balish E: Antifungal therapy of dermatophytosis in guinea pigs and congenitally athymic rats. Mycopathologia 90:47-54, 1985 Zajac A, Williams JF, Williams CSF: Mange caused by Trixacarus caviae in guinea pigs. JAm Vet Med Assoc 177:900-903, 1980 Zenoble RD, Greve JH: Sarcoptic mite infestation in a colony of guinea pigs. J Am Vet Med Assoc 177:898-900, 1980 Zwicker GM, Dagle GE, Adee RR: Naturally occurring Tyzzer's disease and intestinal spirochetosis in guinea pigs. Lab Anim Sci 28:193-198, 1978
Amgen Inc. 1900 Oak Terrace Lane Thousand Oaks, California 91320
0195-5616/87
$0.00+ .20
Guinea Pig Husbandry and Medicine
Lynn C. Anderson, D.V.M.*
The guinea pig, or cavy (Cavia porcellus), first become popular as a pet during the 16th century, when Dutch explorers introduced this native South American rodent to European fanciers. Its earliest domestication has been traced to the Andean Indians of Peru, who used guinea pigs as a food source. Guinea pigs were also used as sacrificial offerings to Incan gods. Much of the literature on guinea pig biology and medicine has resulted from their use as research animal models. Since 1780, when Lavoisier used guinea pigs to measure heat production, they have been used in a wide variety of scientific applications. The most notable of these uses include nutrition, toxicology, and immunology. Their large tympanic bullae and classic response to sound have also made guinea pigs particularly useful for auditory research.
ANATOMY Guinea pigs are relatively compact, have virtually no tail, and are taxonomically related to the chinchilla and porcupine. They display a wide variety of coat types and colors. The most commonly seen pets are the shorthaired, smooth-coated English or American varieties, the long, silky-haired Peruvian, and the short, wire-haired Abyssinian. The latter breed may look unhealthy, as its coat is arranged in whorls or rosettes, giving it a ruffled, untidy appearance. Several outbred stocks and inbred strains 2 and 13 have been developed primarily for research purposes. A hairless guinea pig has been recently developed for research in transdermal drug penetration and other studies in which hair may interfere with research efforts. Various coat colors, including white, red, tan, brown, chocolate, and black, may be exhibited singly in monochromatic animals or as bands or patches in bicolored or tricolored specimens. · ' In a healthy guinea pig, the hair has a low luster. Tactile hairs are arranged in five to six rows on the muzzle, with two pairs around the eye. The triangular oral opening is small, making inspection of the oral cavity *Diplomate, American College of Laboratory Animal Medicine; Manager, Veterinary Research , Amgen Inc. , Thousand Oaks, California
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Figure 1. Male (boar) genitalia showing digital extrusion of the penis. The scrotal sacs, which are separated by the anal opening, lie below the penis.
difficult without sedation or anesthesia. Guinea pigs are monogastric herbivores. They have hypsodontic (open-rooted and continuously erupting) teeth, with the pattern of 1/1 incisors, 111 premolars, and 3/3 molars. In the absence of canine teeth, there is a diastema between the chisel-like incisors and the flat premolars and molars. The latter teeth are used for grinding; consequently, the masticatory muscles are well developed. Other distinguishing external features include the forefeet, which have four toes each, and the hindfeet, which have three toes each. Both male and female guinea pigs have one pair of inguinal nipples, although only the female has mammary glands. The male's penis is normally retracted and opens slightly ventral to the anus. Sex identification may be accomplished by palpating the penis or testes or by gently retracting the preputial skin to extrude the penis (Fig. 1). The female normally has an intact vaginal closure membrane, which lies in a shallow U-shaped fold between the anus and urethral opening (Fig. 2). During estrus and parturition, this membrane is perforated. Postmortem examination of a normal, healthy guinea pig reveals several characteristics of comparative interest. Unlike stomachs in other rodents, the guinea pig's stomach is nonglandular, and the closely associated spleen is relatively broad. Females have significantly larger and heavier spleens than males. As is typical of herbivores, much of the digestive process occurs in the cecum, which may contain up to 65 per cent of the gastrointestinal
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orifice Vaginal orifice
Figure 2. Female (sow) genitalia showing the urethral orifice, the vaginal orifice (covered by a membrane), and the anal opening.
contents. The adrenal glands are relatively large, bilobed, and triangular. The inguinal canals, which contain the testes, remain open throughout life. The male's coiled, tubular vesicular glands lie ventral to the ureters and extend approximately lO em into the abdominal cavity from their base in the pubic area. These glands should not be confused with the female's bicornate uterine horns.
BEHAVIOR The docile temperament and lack of objectional odor of guinea pigs enhance their acceptability as pets. They seldom bite or scratch if handled frequently and gently. When startled by a loud noise, sudden movement, or strange environment, guinea pigs may freeze and maintain position for up to 20 minutes or scatter and leap. Guinea pigs vocalize when frightened by making a series of short calls (chutters), whining, or whistling. When frightened, guinea pigs scatter their bedding and food, push ingesta into sipper tubes, and foul food and >Vater. Groups of guinea pigs establish a social hierarchy with one dominant (alpha) male. Animals of lower rank may develop hair loss from fur chewing (barbering) by the more dominant members. Young animals may pull hair
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from their dams. However, pregnant sows often lose hair during the later stages of gestation, and weaning guinea pigs may develop thin hair as their neonatal fur drops out and is gradually replaced by mature hair. The sick guinea pig commonly is immobile and has dull, moist eyes and a nasal discharge. REPRODUCTION
For successful breeding programs, guinea pigs may be housed in pairs or harems of 4 to 10 females per male. Females should first be bred between 3 and 7 months of age. After 7 months, the pelvic symphysis may be permanently fused; parturition may be complicated by dystocia and, ultimately, maternal and fetal deaths. The first estrus is significantly less fertile than subsequent matings. Although males may display sexual behavior as early as 30 days of age, fertile matings will not be achieved until 3 to 4 months of age or at 550 to 600 gm body weight for males and 350 to 450 gm body weight for females. Spontaneous ovulation occurs approximately 10 hours after the onset of estrus, which is characterized by perforation of the vaginal membrane. This membrane reforms after ovulation. The normal estrous cycle is 16 days, and estrus lasts an average of 8 hours. A fertile postpartum estrus occurs 6 to 15 hours after parturition. Artificial insemination has been used successfully in guinea pigs. Ideally, the semen should be deposited at the onset of estrus because late fertilization will result in increased numbers of abortions, stillbirths, or decreased litter size. The guinea pig has an unusually long gestation compared with other rodents. The length of pregnancy will vary from 58 to 72 days and is inversely related to litter size. Fetuses may be palpated as early as 15 days postconception. During late pregnancy, the sow's abdomen will be grossly distended, and she may double in weight. The prominent sign of impending parturition is the separation of the pubic symphysis during the last week of pregnancy. The separation increases to 3 em during the final prepartum hours. Because gestation length is variable and no nests are built, the onset of parturition is unpredictable. Delivery of the young normally takes 30 minutes, with 3 to 7 minutes between pups. Dystocias may occur in sows bred for the first time after 7 months or if fetuses are large. Dystocia should be suspected if the sow becomes depressed or produces a greenish-brown vaginal discharge. Digital manipulation of the neonate or caesarean section may be performed. , The relatively long period of in utero development produces young that are nearly self-sufficient and weigh 60 to 100 gm at birth. Young weighing 50 gm or less rarely survive. Newborns are ambulatory, fully furred, and have erupted teeth and open eyes. Despite the presence of only two nipples, a sow may successfully raise five or six offspring. The young may begin to eat solids and drink water from a bowl within several hours of birth, but they should continue to nurse for 14 to 21 days.or until they weigh 180 gm. If necessary, hand rearing of neonates over 60 gm is possible, but hand
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rearing should not begin until12 to 24 hours postparturition. Fortified guinea pig food, softened with milk or water, may be used for this purpose, but it may not sustain normal growth. Lactating sows will readily nurse offspring from another litter, and older young will strip all sows in a colony. Young should nurse at least 15 days, but they begin eating solid food at 2 to 3 days.
MAINTENANCE
Guinea pigs are often presented with nonspecific complaints of decreased alertness and activity, depressed appetite, or weight loss. The case history should include a thorough review of the animal's normal habitat and diet and the owner's husbandry practices because many diseases are the consequence of improper maintenance. Antibiotic therapy is often contraindicated because it may induce lethal effects. Therefore, preventive measures are critical to the animal's survival. Anorexia, a common nonspecific sign in guinea pigs, is treated with force-fed meals of a slurry of yogurt, guinea pig food, vitamin C, ground guinea pig fecal pellets, and treatment for the specific malady. In the wild, guinea pigs live in open, grassy habitats or burrows that were excavated, then deserted, by other animals. The group normally feeds and rests together at time intervals based on day length and ambient temperature. Cage Design Domestic guinea pigs are hardy, inexpensive, and fairly easy to maintain in mixed groups, pairs, or as individuals. In general, their habitat should be easy to clean and should protect the animals from injury or drafts. The cage or pen should provide adequate floor space, which is estimated per animal at 101 square inches for adults or 180 square inches for breeders. Overcrowding is associated with decreased reproduction and increased hair chewing. The walls of an enclosed cage should be at least 7 inches high. The sides of an open pen should be 10 inches high to prevent the animals, especially males, from escaping. The habitat may be constructed from solid plastic or stainless steel slats or wire mesh. Wood should be avoided because it is difficult to clean, and galvanized metal tends to rust and corrode. When wire mesh is used for flooring, it should form %-inch squares or 0.5- X 3.0-inch rectangles to provide adequate footing. Some breeders prefer wire mesh b<:;cause it allows urine and fecal pellets to drop through, thus protecting the animals from contact with wet, soiled bedding. However, wire mesh has been associated with hair loss, footpad ulcers, and decreased breeding and weight gain. Young guinea pigs raised in solid-bottom cages do not adapt well to mesh and may develop severe foot injuries or fractured legs. Solid-bottom cages with bedding provide more warmth and protection. Wood shavings or shredded paper are preferable to sawdust, which may form _an impaction around the penis and inhibit copulation.
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Temperature and Humidity Guinea pigs do well in a stable environment in which the temperature is maintained at a constant level ( ± 2°F) within a range of 65 to 75°F (18 to 24°C). Their compact size allows them to tolerate cold more readily than high ambient temperatures. The room humidity may be maintained between 40 per cent and 70 per cent, although 50 per cent is considered ideal. Both the temperature and humidity within a cage may vary considerably from room values, depending on the construction and bedding materials, number of animals, level of sanitation, and ventilation rate. High temperatures may interfere with reproduction, and cool, moist environments may predispose the animals to respiratory infections. Sanitation Frequency of sanitization will depend on housing construction and animal population per unit. Solid-bottom cages must be cleaned more often than those with wire mesh or slatted floors, which allow urine and feces to pass through into collecting pans. In general, cages should be cleaned and sanitized once a week. Water containers and feeders may require more frequent cleaning, especially if the animals urinate and defecate in them. Guinea pigs also tend to contaminate water bottles by chewing on the sipper tubes and clogging them with food particles. Sanitation may be accomplished with a hypochlorite solution or detergent; a vinegar or other weak acid solution will aid in removing scale deposited by crystalline urine. Regardless of the products used, the cages should be thoroughly rinsed with clean water. If bedding is used, the cages should first be dried, and the depth of bedding should not extend to the level of the sipper tube or it will act as a wick and drain the bottle.
NUTRITION
In their native habitats, guinea pigs feed on grasses, roots, fruits, and seeds. The dietary requirements for laboratory guinea pigs have been established by the National Academy of Sciences and may be adapted for pet animals. Guinea pigs do not adapt well to changes in diet or readily accept salty, bitter, or sweet rations. Complete, highly palatable diets containing 18 per cent to 20 per cent protein, 4 per cent fat, and 16 per cent fiber produced the highest level of nonspecific immunity factors in one study. Many of the required vitamins are produced by the intestinal microflora. The role of coprophagy in nutrition is unclear, but pr,evention of fecal ingestion has caused weight loss and altered mineral excretion. Unlike most mammals, guinea pigs require a high level of folic acid. Like primates, they are also dependent on a dietary source of vitamin C because of an absence of L-gulonolactone oxidase. Approximately 800 to 1500 mg of vitamin C are added per kilogram of fortified rations. Despite appropriate food storage in a cool, dry area, vitamin C is degraded to approximately 50 per cent of the postprocessing levels within 6 weeks. Deterioration in water, especially in dirty and lighted containers, occurs in
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Table I.
General and Reproductive Data'a.zt.2:3.30.35.38
Adult body weight Male Female Life span Average Maximum Rectal temperature
900-1200 gm 700-900 gm 3-4 yr 6-7 yr 37.9-39.5°C 100.2-103.1°F 90-150/min 230-320/min
Respiration rate Heart rate Blood volume
69-75 ml/kg body wt (4.5-8.3% BW)
Reproductive data First estrus (average) First breeding Male Female Estrous cycle Estrous length Gestation Litter size Average Maximum Breeding life span
68 d 600--700 gm (3-4 mo) 350-450 gm (2-3 mo) 15-17 d 8.2 hr 58-72 d (average, 68 d) 3-4 6-7 18-20 mo
hours or a few days . Fortified diets over 90 days since milling, or those containing less than 200 mg of vitamin C per kilogram diet, should be discarded or supplemented with 10 mg of vitamin C per kilogram body weight per day (20 mg per kg per day for pregnant or lactating animals). This may be accomplished by feeding a handful of fresh , cleaned kale or cabbage on a daily basis. Alternatively, 200 mg of ascorbic acid may be added to each liter of drinking water. These levels are based on an average food consumption of 6 gm per 100 gm body weight per day and water consumption of 10 ml per 100 gm body weight per day. The practice of supplementing fortified pelleted diets with hay or greens is controversial. Productivity may be improved when hay is provided. In one study, neonatal deaths and postweaning culls were reduced after greens were eliminated. Others have claimed that hay helps prevent overgrown teeth and behavior problems such as barbering. Dirty hay or moldy fruit and vegetable supplements are potential sources of microbial pathogens.
PHYSIOLOGY As in other species, the guinea pig's genetics, age, reproductive status, microflora, environment, and diet will influence its physiologic parameters. Many reference texts provide normal data or, more appropriately, "approximate values," which are summarized in Table 1. The si-te and techniques used for blood collection, as well as the methodology and instrumentation
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employed for analysis, will also affect hematology and serum chemistry values . Small blood samples are most readily collected by clipping a toenail or from the retro-orbital sinus. It is more difficult to collect larger samples from the femoral artery or vein. Cardiac puncture is impractical in clinical situations because of the high degree of risk involved. The erythrocyte count increases with age, whereas the reticulocyte count decreases. The erythrocytes are less fragile than those in dogs, but more fragile than those in cats or ruminants. The most prevalent leukocytes are lymphocytes. Neutrophils contain red granules in the cytoplasm. The differential evaluation should include a unique mononuclear cell, known as the Kurloff cell. This cell, characterized by its large mucopolysaccharide eosinophilic intracytoplasmic inclusion body, originates primarily in the spleen. It is commonly classified as a leukocyte and is thought to offer fetal protection from sensitized lymphocytes and IgM molecules. Both endogenous and exogenous estrogen will increase the number of Kurloff cells in the peripheral blood. CLINICAL EXAMINATION AND RESTRAINT The initial clinical examination should be conducted in a quiet room, taking care not to make sudden movements or loud noises that will elicit the characteristic freeze or scatter response. The animal should be placed in a box or cage and observed for coat condition, stance, and attitude. Physical examination requires minimal restraint. The animal should be lifted from its container by grasping it gently under the thorax with one hand and supporting the hindquarters with the opposite hand. Lung and liver injuries and diaphragmatic hernias have been associated with excessive pressure around the abdomen and thorax. The chest is easily auscultated, and the abdomen may be gently palpated. A lighted otoscopic speculum or tube is useful for examining the oral cavity of a sedated guinea pig. DISEASES The guinea pig is susceptible to a number of naturally occurring and experimentally induced diseases. Only those of clinical significance are reviewed in the following section. Bacterial Diseases
Integumentary. Cervical lymphadenitis or "lumps",is most frequently caused by Streptococcus zooepidemicus, although Streptobacillus moniliformis has been rarely isolated from cervical abscesses. Streptococcus zooepidemicus may also cause generalized abscesses, septicemia, uterine infections, panophthalmitis, and otitis media. Transmission most likely occurs via oral lesions caused by coarse food , such as hay , or skin abrasions from fighting, or in an improperly maintained environment. Aerosol infections have been induced experimentally. Fluctuant subcutaneous masses noted in the ventral cervical region involve primarily the submaxillary lymph nodes
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and may interfere with deglutition. Abscesses may rupture spontaneously, exuding a thick, creamy yellowish-white pus. Microscopic examination of this material, collected from the peripheral surface, should reveal chains of gram-positive cocci. Antibiotic therapy will be ineffective if the abscesses are well encapsulated. Surgical drainage and abscess removal may be successful, but intervention may produce septicemia, causing suppuration and abscessation in many organs. Pododermatitis, caused by Staphylococcus aureus, is another clinical problem associated with poor environmental conditions, particularly fecal contamination of wire-bottom cages. This condition is most often seen on the forefeet of obese animals. Firm, ulcerated masses up to 3 em in diameter develop on the feet, causing the animals to shift weight and become relatively inactive. Chronic infections may lead to osteoarthritis and amyloidosis of the kidney, liver, spleen, and adrenal glands. Local or systemic antibiotic therapy or bandaging may help, but the habitat must be clean and smooth. Staphylococcus aureus was isolated from a group of guinea pigs with erythematous skin on the ventral abdomen and thorax, followed by exfoliation of the epidermis. Most of these cases occurred in pregnant animals. Respiratory. Pneumonia is one of the most common bacterial diseases of guinea pigs. Bordetella bronchiseptica, Streptococcus pneumoniae, and Klebsiella pneumoniae may be cultured from the respiratory tract of asymptomatic guinea pigs, but under suboptimal conditions, nutritional deficiencies, inadequate ventilation, high humidity, and temperature extremes, the animal is predisposed to diseases caused by these organisms. Animals may die without premonitory signs. In advanced, chronic cases, breathing is labored due to bronchopneumonia and lung consolidation. Purulent nasal discharge is usually associated with Klebsiella infection. Bordetella bronchiseptica and pneumococcal infections may also cause conjunctivitis, otitis media, stillbirths, and abortions. Culture and identification are required for definitive diagnosis of the causative agent. Treatment of sensitive strains with antibiotics may control the disease but will not eliminate the carrier state. Antibiotic therapy may also produce a variety of toxic signs, which are detailed later in this article. A killed bacterin has been used to eliminate B. bronchiseptica from one large research breeding colony, and Tribrissen given at 10 mg per kg subcutaneously (SQ) has been used successfully for treating pneumonia. The prognosis remains poor. Protection against this bacterial infection has been accomplished with an intranasal vaccination, using a temperature-sensitive mutant. Rats and rabbits may harbor B. bronchiseptica in their respiratory tracts; therefore, these animals should not be housed with guinea pigs. Pasteurella, Actinobacillus, and Pseudomonas aeruginosa have been infrequently associated with pneumonia of guinea pigs. Auditory. Otitis media is frequently associated with respiratory infections, but it is often clinically inapparent. A retrospective survey of 1373 guinea pig necropsies at one institution indicated a 13 per cent incidence of otitis media. The bacteria most commonly isolated were Streptococcus pneumoniae (20 per cent), S. zooepidemicus (15 per cent), B. bronchiseptica (12 per cent), and P. aeruginosa (II per cent). Radiology of the tympanic bullae was 96 per cent accurate and superior to otoscopy for diagnosis. Extension into the inner ear may produce torticollis, ataxia, rolling, or circling.
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Gastrointestinal. Enteric Salmonella infections are most commonly caused by S. typhimurium or S. enterititis, which are introduced through fecal contamination of green vegetables and water. These organisms may produce an acute, fatal septicemia. Animals often die without clinical signs or following nonspecific signs of lethargy and emaciation. Diarrhea is uncommon. Postmortem lesions may be absent in acute cases. Splenomegaly, lymphadenopathy, and liver and spleen necrosis are seen in subacute and chronic cases. Granulomas may also be evident in liver, spleen, lungs, small intestine, and uterus. Fecal culture may be useful antemortem; postmortem isolation from the spleen is more reliable. Antibiotic therapy may stop an epizootic, but will not eliminate carriers. In a colony situation, it is best to depopulate and disinfect, although a mass fecal monitoring program was used successfully to eliminate the disease in a valuable research colony. Bacillus piliformis, Campylobacter, Escherichia coli, and Yesinia pseudotuberculosis have been infrequently associated with enteric disease characterized by wasting and diarrhea. Reproductive. Bacterial mastitis is often a fatal disease caused by E. coli or, less frequently, Klebsiella, S. zooepidemicus, or Proteus. In the male, preputial dermatitis results from trauma, followed by swelling and ulceration of the prepuce and perineum. In one case report, unidentified bacterial colonies were detected by histologic examination of these areas. Treatment with thorough daily cleaning and application of zinc-oxide ointment to the perineal area has been successful. Viral Diseases
Most viral infections of guinea pigs are mild or inapparent. These diseases are seldom of clinical significance, but they may serve as valuable models of human disease, or they may complicate unrelated research projects. Spontaneous, transplantable lymphatic leukemia has been reported in guinea pigs with moderate to marked lymphocytosis, lymphadenopathy, splenomegaly, and hepatomegaly. Hindlimb paralysis and progressive flaccid paralysis have been observed in animals with polio virus and lymphocytic choriomeningitis infections, respectively. In one colony, an epizootic oflethal pneumonia was attributed to an adenovirus. A mild, transient conjunctivitis of juvenile guinea pigs is caused by a chlamydia. This agent produces characteristic cytoplasmic inclusions in conjunctival epithelial cells. Mycotic Diseases Most mycotic infections are dermatophytoses caused by Trichophyton mentagrophytes. Young animals are generally more susceptible than adults. Guinea pigs may be asymptomatic carriers or have areas of patchy alopecia on the face, nose, and ears. These areas may extend along the dorsal trunk and develop into hyperkeratotic lesions with vesicles around the periphery. This organism will not fluoresce under ultraviolet light. Provisional diagnosis is accomplished by microscopic examination of keratinized epithelial cells or affected hair surfaces and identification of arthospores and hyphae. Cultures should be held a minimum of 3 weeks fot: definitive diagnosis. Successful treatment with topical or systemic griseofulvin therapy has been reported, although high infant mortality was associated with oral adminis-
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tration in one colony. Orally administered tolcidate and tolnaftate were effective in a controlled study. Moldy hay has been incriminated as the source of phycornycoses in young guinea pigs. Candida albicans is present in the normal gastrointestinal flora and may cause mild, transient conjunctivitis in young guinea pigs. Endoparasites Few clinical symptoms are associated with endoparasites. A large variety of protozoa normally inhabit the cecum and colon, and complications due to these organisms are generally associated with either poor husbandry or severe debilitation from other causes. Coccidiosis caused by Eimeria caviae may cause weakness, ~maciation, and severe diarrhea, but the disease normally responds to sulfonamide therapy. Cryptosporidia rarely cause diarrhea. Serologic surveys suggest that Toxoplasma gondii infection is more prevalent than pathologic evidence of infection would indicate. Klosiella cobayae are occasionally detected on postmortem histologic examination of the kidneys, but these coccidia cause no clinical signs. Renal and brain lesions have been infrequently reported in guinea pigs infected with Encephalitozoan. Housing guinea pigs with Encephalitozoan-infected rabbits should be avoided. Paraspidodera uncinata is a short (11 to 28 mm) nematode that may be found in the cecum but is not usually pathogenic. Injectable levamisole has been used successfully to control this pinworm infection. Experimental and natural infections with the trematode Fascioloides have also been reported. Eetoparasites Lice are easily detected upon close examination of the fur, where both adults and eggs attach to the hair shaft. Gliricola porcelli is more common than Gyropus ovalis, the latter having a smaller, less rounded head than the former. The mouth parts are used to abrade the skin and harvest cutaneous fluids. The mid- and hindlegs of these lice bear tarsi with only one or no claws. Heavy infestations cause alopecia and pruritis, and infestations may be effectively treated with lindane or malathion dusts. A sarcoptid mite, Trixacarus caviae, has been reported in pet guinea pigs with mixed clinical histories. In one instance, the guinea pigs had hyperkeratotic skin, with or without alopecia, and no pruritis. All areas of the body, except the lower limbs, were affected. In another report, the guinea pig displayed intense pruritis, characterized by self-inflicted wounds and furious running and circling. Identification of the mite may require repeated skin scrapings miXed with 10 per cent potassium hydrpxide. Treatment may be accomplished with shampooing, followed by exposure to dichlorvos strips 1 day a week for 6 weeks, diluted 1:40 lime-sulfur baths, or once weekly applications of 10 per cent lindane for 3 weeks. lvermectin injectable at 200 mg per kg SQ is a useful treatment for ectoparasitism. Heavy infestations of the mite Chirodiscoides caviae may also cause pruritis and alopecia, but it is generally considered to be harmless. Other mites have been rarely identified in guinea pigs, includil)g Demodex caviae, Sarcoptes scabei, and Notoedres muris.
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Nutritional and Metabolic Disorders Guinea pigs have been used as a model for many nutritional studies; however, only those of clinical significance are included in this article. The guinea pig's dependence on exogenous vitamin C and the vitamin's labile characteristics make these animals particularly susceptible to scurvy. Clinical symptoms of scorbutus include inappetance, diarrhea, reluctance to move, swollen, painful joints, impaired or deformed bone and teeth formation, gingival, costochondral, and muscle hemorrhages, and delayed wound healing. Secondary infections are common and presumably are the result of depressed phagocytic activity caused by vitamin C deficiency. Response to treatment is dramatic, provided that the animals are given sufficient daily quantities (25 mg per kg) of the vitamin until recovery and until the predisposing factors are corrected. Widespread metastatic calcification of soft tissues may cause lameness, or they may be found incidentally on postmortem examination. This condition is secondary to an alteration in the complex relationship among calcium, phosphorus, magnesium, and potassium. Experimental diets high in cholesterol have caused hemolytic anemia. Malocclusion of premolar teeth causes a syndrome commonly known as slobbers. Animals are inappetant, lose weight, and have moist skin around the mouth, chin, and ventral neck. The mandibular molars are overgrown in the lingual direction, and the maxillary molars are excessively worn. Subacute scurvy and chronic fluorosis may cause similar clinical signs and should always be considered. Spontaneous, contagious diabetes mellitus has been reported in one colony. These animals have elevated glucose-tolerance test values and glycosuria. Pregnancy toxemia is most often seen during the first or second gestation of obese, stressed guinea pigs. Clinical signs develop 7 to 10 days prior to parturition and may include nonspecific signs such as lethargy and anorexia. Blood glucose is markedly decreased, and urine pH is acidic and contains protein. Rapid mobilization of lipids leads to ketosis, coma, and death. The primary cause may be inadequate blood flow through uterine arteries. Antibiotic Toxicity From a clinical standpoint, the guinea pig's marked, often lethal sensitivity to antibiotic therapy cannot be overemphasized. The predominant gastrointestinal microflora are usually gram-positive anaerobic cocci and lactobacilli. Escherichia coli are normally absent or present in small numbers, as are Clostridia. Antibiotics alter the normal microflora and may cause an enterotoxemia and consequent clinical signs. Agents that have been reported to cause enterotoxemia include penicillin, ampicillin, bacitracin, erythromycin, spiramycin, streptomycin, lincomycin, gentamicin, clindamycin, vancomycin, and (variably) tetracycline. As little as 50,000 units of penicillin given intramuscularly (IM) will cause 20 to 100 per cent mortality within 3 to 5 days. Topical antibiotics have also produced the lethal syndrome. The animals appear normal for 24 to 48 hours, tnen become active, anorexic, and hypothermic. Some may have diarrhea. By 72 hours, the gait is unsteady,
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GUINEA PIG HUSBANDRY AND MEDICINE
Table 2.
Therapeutic Drug Dosages ANTIMICROBJALS7• 18•23
Agent
Dose
Route
Sulfamethazine
PO
Chloramphenicol sodium succinate
1 mg/ml drinking water up to 60 days 12.5 mg/kg, once a day for 5-14 days 5 mg/kg, twice a day for 4 days, may repeat after 4 days withdrawal 30 mg kg, twice a day for 5 days
Agent
Dose
Route
Indications
Sulfamethazine
1 gm/L drinking water for 5 days 0.25 gm/L drinking water for 30 days 25 mg!kg, once only 0.1% spray, 5% dust 1% dip, once a week for 3 weeks 1:40 dilution with H,O, bath
PO
Coccidia
PO
C ryptosporidium
SQ Topical Topical
Parasidodera
Topical
Mites
Cephaloridine Oxytetracycline
IM 1M
IM
ANTHELMINTICS 10• 18•30•42 •43
Sulfaquinoxaline Levamisole Malathion Lindane Lime-sulfur
Lice Mites
OTHER37
Agent
Dose
Route
Indications
Griseofulvin
15 mg!kg once a day for 14-28 days
PO
Trichophyton
respiration increases, and the animals become prostrate shortly before death. The most common postmortem lesions are colitis and a distended, fluid- and gas-filled cecum. A less frequently seen hemorrhagic syndrome has been reported in animals that suddenly die with visceral hemorrhages, leukopenia, and thrombocytopenia. Chronically administered, low doses of antibiotics may cause stunted growth, alopecia, and neurologic signs. The pathogenesis of antibiotic toxicity is not fully understood, but it is associated with an increase in the number of coliforms and anaerobic rods (Clostridium), along with a decrease in anaerobic gram-positive organisms. Toxicity may be caused by absorption of E. coli-produced endotoxin or clostridial enterotoxins. Systemically administered chloramphenicol, cephaloridine, low doses of sulfonamides, topical neomycin, and polymixin B have been used successfully to counter lethal antibiotic effects. Parenteral tetracycline used for 3 to 4 days or on alternate 4-day periods may be tolerated for therapy of infectious disease. Suggested drug dosages are listed in Table 2.
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LYNN
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ANDERSON
NEOPLASIA Most neoplasms are found incidentally on postmortem examination. In one survey, nearly one third of all tumors were found in the respiratory tract. The neoplasms most likely to be encountered clinically are the benign skin tumor trichofolliculoma or leukemia. ANESTHESIA AND EUTHANASIA Sedation or anesthesia may be required to facilitate physical examination, radiography, or sample collection. The most common surgical procedures are superficial skin incisions or excisions, caesarean sections, and castrations. The recommended dosages are described in the article "Anesthesia and Surgery of Laboratory Animals," but responses are extremely variable. Self-mutilation of distal limbs has been associated with parenteral administration of lnnovar-Vet and ketamine hydrochloride. Furthermore, ketamine provides poor analgesia and muscle relaxation. Ether causes marked salivation and is flammable. Although the use of ether is discouraged, if it is used, it should be preceded by atropine sulfate administration. Methoxyflurane is the inhalant anesthetic of choice. Euthanasia may be accomplished by administering overdoses of barbiturates or by giving one of the commercially available injectable euthanasia agents intraperito~eally. PUBLIC HEALTH SIGNIFICANCE A number of organisms that infect or inhabit guinea pigs are potentially zoonotic, but these organisms are seldom associated with human disease. These organisms include Salmonella, Campylobacter, lymphocytic choriomeningitis, and Sarcoptes. Allergy to gqinea pig dander is most frequently reported in personnel who have frequent contact with the animals, such as laboratory technicians. Clinical symptoms in human beings include rhinitis, asthma, and skin rashes. Skin tests are not always reliable indicators of sensitivity, but they may be useful in some instances because false positives are rare. ACKNOWLEDGMENTS
The author gratefully acknowledges the assistance of the secretarial and librl!ry staffs and the general support of the Amgen Corporation in the preparation of this article.
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