COMMON SPECIES KEPT IN CAPTIVITY

Guinea pigs, Cavia porcellus, are members of the Caviidae family of the order Rodentia. Guinea pigs are native to mountainous regions of South America where they were domesticated as long as 3000 years ago. Wild species of guinea pigs, or cavies, still inhabit Columbia, Peru, Venezuela, Argentina, Brazil, and Paraguay. Domesticated cavies in these countries are used for food. In the wild, guinea pigs live in small groups and, therefore, are often more comfortable in the presence of other guinea pigs when maintained as companion animals.

Extensive breeding has resulted in numerous varieties of coat color and characteristics. The most common breeds are the American (or English) which has a short, smooth coat and the multicolored Teddy (Figure 17-1); Abyssinian (Figure 17-2), which has a medium length coat in a whorled pattern; and the Peruvian, which has a very long, smooth coat.

Figure 17-1 Two common guinea pig breeds: Teddy (left) and American (right).

Figure 17-2 Abyssinian guinea pig.

BIOLOGY

Guinea pigs have wide bodies with short limbs. A distinctive anatomic characteristic of species in the family Caviidae is the number of digits on the front and rear feet (4 digits front feet and 3 digits rear). Tails are usually very short or absent. The guinea pig has a short, flat nose, laterally placed eyes, and hairless external pinnae. Adult guinea pigs usually weigh between 700 and 1200 g, with the males being slightly larger than females. The average life span of the companion guinea pig is approximately 5 to 7 years.

The dentition of the guinea pig is described as aradicular hypsodont (e.g., all teeth have a relatively long crown and are “open rooted”).¹ The maxilla is slightly wider than the mandible, and the occlusal angle of the premolars and molars is marked compared to other rodent species. The dental formula of the guinea pig is 2(I 1/1, C 0/0, PM 1/1, M 3/3) = 20. The maxillary incisors are much shorter than those set in the mandible. The molars and premolars are not easily visualized without special instrumentation because of the small size of the oral cavity and tendency for the involution of the buccal surface.

Females are sexually mature at 6 weeks of age, whereas males on average reach puberty approximately 4 weeks later. Gestation is long, when compared to other rodents, at 68 days.² As a result of this long gestation period, young are precocial when born. Juvenile pigs usually eat solid foods by 4 or 5 days of age.³ Litter sizes range from 1 to 6, with an average of 3 to 4 young.² A female guinea pig should deliver her first young before she is 6 months of age. If birth has not occurred before 6 months of age, the pubic symphysis becomes mineralized, with future pregnancies resulting in an inability of the sow to naturally deliver the babies. Female guinea pigs that become pregnant after 6 months of age invariably require cesarean section deliveries.

HUSBANDRY

PREVENTIVE MEDICINE

In the United States, guinea pigs are not routinely vaccinated for infectious diseases. However, owners should be encouraged to have annual examinations that include an oral examination and a complete blood count. Being prey species in the wild, guinea pigs are adept at hiding illness, and routine evaluations by a qualified veterinarian may help in detecting abnormalities early.

Many health problems of guinea pigs are related to improper husbandry. During a routine veterinary visit, the owners should be asked to provide a detailed description of the animal’s housing environment, including substrate, frequency of cleaning, ambient temperature, and exercise time. The diet history is also important. Owners should be asked not only what the guinea pig is offered, but also in what proportions and of what foods the animal actually eats.

RESTRAINT

Most guinea pigs are quite docile and do not require aggressive restraint. Often a hand on the animal’s dorsum is adequate to restrain a guinea pig patient on the examination table (Figure 17-3). When transporting a guinea pig, support the body with one hand under the thorax and abdomen while placing the other hand on the back to prevent the patient from falling or jumping (Figure 17-4).

Figure 17-3 Restraint of a guinea pig patient for examination.

Figure 17-4 Restraint of a guinea pig patient for transport.

If chemical restraint is required, gas anesthesia with isoflurane or sevoflurane is generally well tolerated. Anesthetic gases can be delivered via mask or induction chamber. Mild sedation can be achieved with an intramuscular injection of a combination of midazolam (0.2-0.5 mg/kg) and butorphanol (0.2-0.5 mg/kg) intramuscularly.

PERFORMING A PHYSICAL EXAMINATION

Guinea pigs often do not exhibit clinical signs early in a disease process. Therefore, a thorough physical examination can be extremely useful in determining the overall health status of the animal. Before beginning a physical examination, it is important to observe the animal before it has been stressed by restraint. A healthy guinea pig should be alert and aware of its surroundings. As guinea pigs are often shy animals, they may attempt to hide or escape. The examiner should use a thorough, systematic approach to focus on the respiratory character and rate, posture, and attitude of the animal. It is also important to have any instruments (e.g., transilluminator, stethoscope, thermometer, blood-collecting supplies) that may be necessary to decrease the amount of handling time for the patient.

Obtaining an accurate body temperature, heart rate, and respiratory rate is best accomplished at the beginning of the examination, as these parameters will invariably change with handling. An accurate weight should be obtained using an electronic gram scale. A “hands-on” physical examination should begin with the head; the veterinarian should assess the eyes for symmetry or discharge and check that the external pinnae of the guinea pig are hairless, as normal. The external ear canals often contain a small to moderate amount of dark, ceruminous debris. The nasal planum should be dry and flat, whereas palpation of the ventral mandible may reveal deformities secondary to overgrowth of molar and premolar apices.

The guinea pig coat varies somewhat with breed but, in general, should be smooth and shiny. Guinea pigs often have a mild to moderate amount of dark sebaceous debris on the skin of the dorsum. Older male guinea pigs may develop a focal accumulation of this debris at the base of the vertebral column, which may be referred to as the “grease gland.”⁴

Thoracic auscultation and abdominal palpation can be performed as in other patients. Heart and respiratory rates will vary depending on the degree of stress a patient experiences. As pulse and respiratory rates can be very rapid, careful auscultation is necessary to detect subtle abnormalities (e.g., murmurs, crackles, wheezes). Auscultation of gut sounds is also an important part of the guinea pig physical exam. A healthy guinea pig should have 1 to 2 borborygmi per minute. The practitioner should keep in mind that stress will decrease gastrointestinal (GI) motility; therefore, a stressed animal will often have a decrease in borborygmi. Structures normally found on abdominal palpation include kidneys, urinary bladder, cecum, and intestines. Fecal pellets are often palpable in the colon. Careful examination may reveal the presence of abnormalities such as GI distention, masses, or, in females, ovarian cysts. Limbs and joints should be carefully evaluated because thickened or painful joints may be indicative of a vitamin C deficiency.

A complete oral examination is an important part of the guinea pig exam. Because of the potential stress associated with the oral exam, this evaluation should be reserved for the end. The oral cavity of the guinea pig is very narrow with a small opening, making visualization difficult (Figure 17-5). Instruments such as an otoscope with cone or a human nasal speculum will increase visualization of the caudal oral cavity (Figure 17-6). However, many dental lesions may be overlooked using these methods, and anesthesia is often required to adequately determine oral health.

Figure 17-5 The oral cavity of a guinea pig. Note the abundance of soft tissue that obscures visualization of the molars and premolars.

Figure 17-6 Oral examination of a conscious guinea pig using a human nasal speculum on a transilluminator base.

DIAGNOSTIC TESTING

Venipuncture

Obtaining blood samples from guinea pigs for routine diagnostics is a challenging procedure. Peripheral venipuncture sites available for most mammals (e.g., lateral saphenous vein and cephalic vein) are difficult to visualize in guinea pigs and only allow for the collection of small sample volumes. The jugular vein may be used; however, the short neck of the guinea pig and poor tolerance of the aggressive restraint by the patient restrict the availability of this site for blood collection. Often to obtain an adequate blood sample, it is necessary to anesthetize the patient. Once anesthetized, the large central vessels may be accessed with less stress on the patient and phlebotomist. Acceptable venipuncture sites while the patient is anesthetized include the cranial vena cava (Figure 17-7), femoral vein (Figure 17-8), and jugular vein.

Figure 17-7 Blood collection via the cranial vena cava in an anesthetized guinea pig.

Figure 17-8 Blood collection via the femoral vein in an anesthetized guinea pig.

Imaging

Whole body radiographs may provide a large amount of information for the veterinarian treating an ill patient. Both lateral and ventrodorsal (or dorsoventral) views should be obtained (Figures 17-9 and 17-10). To minimize rotation, care should be taken to extend the limbs symmetrically when positioning the patient. Because guinea pigs have stocky builds with short limbs, and because they resent aggressive restraint, sedation or anesthesia is helpful in obtaining diagnostic radiographs as well as in reducing the patient’s stress (Figure 17-11). Table 17-1 is a guideline for radiographic techniques used in common small mammal radiographic studies.

Figure 17-9 Right lateral radiograph of a guinea pig. Note the moderate overgrowth of the apices of the mandibular molars and premolars, remodeling of ribs, and large amount of ingesta within the GI tract.

(Courtesy University of California–Davis.)

Figure 17-10 Ventrodorsal radiograph of the same guinea pig pictured in Figure 17-9.

(Courtesy University of California–Davis.)

Figure 17-11 Positioning of an anesthetized guinea pig patient for a right lateral radiograph.

TABLE 17-1 Guidelines for Radiographic Techniques for Selected Radiographic Studies in Guinea Pigs

Anatomic location	mA	kVp
Whole body	5.0	44
Extremities	7.5	54
Skull	6.0	48-53

From Silverman S, Tell LA: Radiology equipment and positioning techniques. In Silverman S, Tell LA, editors: Radiology of Rodents, Rabbits, and Ferrets: An Atlas of Normal Anatomy and Positioning, St Louis, 2006, WB Saunders. kVp, kilovolt peak; mA, milliampere.

Dental malocclusion is a common disease problem in guinea pigs. Radiographs of the skull are helpful in assessing the degree of malocclusion as well as potential bone involvement. In addition to lateral and dorsoventral views of the skull, right and lateral oblique views can help to localize lesions. Magnified views of the skull can be obtained by placing the patient on an elevated platform under the x-ray beam without changing the distance between the x-ray cassette and beam.

Ultrasound is another imaging modality that is very useful in the diagnosis of common guinea pig disease processes, such as ovarian cysts (Figure 17-12) and urinary tract calculi. As with radiographs, sedation or anesthesia can assist in reducing patient stress and improve the quality of images. Guinea pigs often have a large amount of gas accumulation in the GI tract, which obscures the ultrasound image, sometimes making this imaging technique of limited value.

Figure 17-12 Ultrasound image of a large ovarian cyst in a mature female guinea pig.

(Courtesy University of California–Davis.)

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