GUINEA PIGS

CHAPTER 17 GUINEA PIGS





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



Housing


Guinea pigs are best housed in well-ventilated, wire-sided cages with solid bottoms. Wire-bottom cages may also be used; however, care must be taken to ensure that the mesh is small enough that a limb cannot become entrapped. An area of solid flooring should be provided, as uninterrupted time on wire mesh may predispose the guinea pig to pododermatitis. Adequate space is needed in the enclosure for the guinea pig to move about unencumbered with enough space for a hide box. Hide boxes or a secluded space is required for prey species (e.g., rodents) to reduce stress that may lead to disease problems. Substrate products that contain aromatic oils (e.g., cedar and pine shavings) should not be used, as they can act as contact and respiratory irritants. Appropriate bedding materials include recycled newspaper products, shredded paper, and aspen shavings. The enclosure should be cleaned thoroughly on a regular basis (e.g., 2 times per week) because unsanitary conditions predispose the guinea pig to pododermatitis, respiratory, and other health problems. If housed indoors, guinea pig enclosures do not require a cover, as these animals do not typically jump or climb. However, the sides of the enclosure should be high enough to prevent escape (approximately 25 cm).2 Heavy food containers are recommended to make dumping of the receptacle more difficult. All food containers should be easy to disinfect and cleaned regularly, as guinea pigs have a habit of soiling their food bowls. Most guinea pigs readily accept drinking water from a sipper bottle, which will decrease spillage and will keep feces, urine, and bedding from contaminating the water.


These animals, native to the Andes Mountains, are very susceptible to hyperthermia and should never be housed in temperatures greater than 80° F. High humidity can also exacerbate a guinea pig’s sensitivity to elevated temperatures by increasing the heat index. All animals are very sensitive to environmental and/or nutritional changes. Therefore, if changes have to be made, gradual exposure of the animal to the changes is recommended.



Diet


An appropriate guinea pig diet includes a formulated, pelleted diet for that species, high-quality hay (e.g., timothy, orchard grass, oat) ad libitum, and ample fresh vegetables. As the animal’s food intake is more dependent on volume consumed rather than calories consumed, a pet fed a predominantly pelleted diet (higher nutritional concentration) has a tendency to become obese. Fruits and grains, if they are offered at all, should comprise a very small portion (<10%) of the total diet and offered only as treats.


Because guinea pigs lack the enzyme L-gulonolactone oxidase, they are unable to synthesize ascorbic acid from glucose. Therefore, guinea pigs require supplemental vitamin C in their diets. Although commercial guinea pig pellets are manufactured with vitamin C, the supplement often degrades rapidly, especially if the pellets are subjected to high heat and humidity. Vitamin C placed in drinking water also degrades rapidly and should be changed daily. To ensure that a guinea pig is receiving a proper amount of vitamin C, it is necessary to supplement a diet of pellets and hay with plenty of fresh foods or often a specifically manufactured vitamin C supplement tablet (Oxbow, Inc., Murdock, NE). Many green, leafy vegetables, such as kale, mustard greens, dandelion greens, parsley, and many others, are excellent sources of ascorbic acid (Box 17-1). The vitamin C requirement of an adult, nonbreeding guinea pig is 10 mg/kg/day.2,3






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.





DIAGNOSTIC TESTING




Hematology


Baseline blood work is an important tool in the routine monitoring of health as well as in the diagnosis of disease. A complete blood count is essential for assessing red blood cell and white blood cell parameters (Box 17-2).



Guinea pigs have heterophils rather than neutrophils as the predominant circulating granulocyte. Heterophils lack myeloperoxidase, the enzyme that causes purulent, liquid exudates. Therefore, the debris contained in guinea pig abscesses is often found to be very thick and caseous, a fact that must be understood when treating these conditions. A normal guinea pig white blood cell differential will consist of primarily heterophils and lymphocytes, usually with a greater proportion of lymphocytes. The remaining leukocyte types (e.g., monocytes, eosinophils, basophils) are normally present in very low numbers. Early stages of a guinea pig’s inflammatory response are often characterized by a shift in the differential white cell ratio (e.g., increased heterophils, decreased lymphocytes) rather than an increase in total leukocyte count. This ratio shift makes evaluating the entire leukogram essential for health evaluation (Box 17-3). The platelet count is also an important marker of inflammation in guinea pigs and other small mammal species. Large increases in the platelet count (>1,000,000/ml) can be seen without an increase in the total white blood cell count.



A cell type that is unique to guinea pigs is the Kurloff cell. These large lymphocytes contain a cytoplasmic inclusion (e.g., a Kurloff body). Kurloff cells are noted most often in the peripheral blood of reproductive age females, although they are also identified in male guinea pigs. The number of circulating Kurloff cells will increase in response to exogenous estradiol and testosterone administration, although the effects were more dramatic with estradiol administration.7,8 Other studies have shown the disappearance of Kurloff cells in spayed female and castrated male guinea pigs.8 The function of the Kurloff cell is not completely understood, and these cells appear to lack lysosomes. At this time, there is no evidence that the Kurloff cell has phagocytic activity.8 The activity of Kurloff cells appears to most closely correlate with that of natural killer cells found in other species.7





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.





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.


Oct 1, 2016 | Posted by in EXOTIC, WILD, ZOO | Comments Off on GUINEA PIGS
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