Biology of the Guinea Pig
Origin and Habitat
The guinea pig or cavy is native to South American, particularly Peru, Argentina, Brazil, and Uruguay. Guinea pigs inhabit a variety of terrains ranging from mountains to grasslands. They are gregarious, living in burrows they make themselves or in abandoned burrows made by other animals. Guinea pigs are nocturnal feeders; the diet consists of various forms of vegetation.
The name "guinea pig" has become synonymous with "experimental subject" in the English language. Most domestic guinea pigs are bread specifically for use in biomedical activities. The most common stocks used in research are the short hair (English and American), Dukan-Hartley, and Hartley. The shorthairs come in a variety of colors; the Dunkan-Hartley and Hartley are albinos. The most common inbred strains used are strain 2 and 13, which are tricolor.
In the 1500s, guinea pigs were introduced into Europe and kept for fancy. Guinea pigs kept as pets come in several coat colors and are available in different "hair styles", those being the English and American with short hair, the Abyssinian with rough hair going in a pattern of rosettes and the Peruvian with long silky hair.
Guinea pigs are also used for food by the Andean Indians.
A guinea pig is lifted by placing one hand around the animals trunk and supporting the hind limbs with the other hand. It is important to support the rear quarters, especially large adult and pregnant animals, in order to prevent injury. With this two-handed technique, the animal can be held securely in any position.
Guinea pigs panic easy in response to a new or frightening experience. Scattering to the corner of the cage or freezing in place for up to 20 minutes may be seen. Teeth chattering of nervous pigs can also be seen.
Anatomy and Physiology
Adult body weight: female: 700-900 g; male: 900-1200 g
Life span: 4-5 years
Respiratory rate: 42-105 breaths/minute
Heart rate: 240-250 beats/minute
Normal average rectal temperature: 103oF
The dental formula is 2(I 1/1, P 1/1, M 3/3) =20. All teeth are open-rooted. The guinea pig rarely, if ever, bites.
The stomach is entirely glandular and not separated into chambers like other rodents. The guinea pig has a large cecum, accounting for up to 65% of the gastrointestinal tract volume.
The left lung consists of three lobes; the right lung consists of four lobes.
The male and female guinea pig has two inguinal mammary glands.
The thymus is located subcutaneously on either side of the trachea and is easily removed surgically. There may also be mediastinal thymic tissue.
The urethra of the female guinea pig generally opens along the ventral edge of the clitoral fossa, but occasionally opens independently below the vulva.
Kurloff cells are unique mononuclear leukocytes (white blood cells) that occur in guinea pigs. These cells contain a large intracytoplasmic inclusion, proliferate during estrogenic stimulation and pregnancy, and may function to protect fetal antigens from sensitized maternal lymphocytes and immunoglobulins.
Guinea pigs have a dietary requirement for Vitamin C, and therefore, should be fed a commercial pelleted diet formulated specifically for guinea pigs. Diets, such as these, are nutritionally complete and do not require supplementation. If supplements are offered, they should not consist of more than 15% of their diet. Water should be provided ad lib.
Food intake is approximately 6 g/100 g BW/day; water intake is approximately 10 ml/100 g BW/day.
Female guinea pigs are called sows; males are called boars. Breeding onset is when the female attains a weight of approximately 500 grams (2-3 months) and males, a weight of approximately 650 grams (3-4 months), although females may have their first estrus at 5-6 weeks of age. Guinea pigs are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 15-17 days and estrus itself lasts 24-48 hours. Vaginal smears are useful for determining the stage of the estrous cycle. Mating is usually nocturnal and can be determined by the presence of sperm on a vaginal smear or the presence of a copulatory plug in the vagina.
Characteristic of hystricomorphs, the female guinea pig has a vaginal closure membrane that is perforated at proestrus/estrus and at parturition.
The average gestation period is 65 days. Relaxin causes the fibrocartilaginous pubic symphysis to disintegrate between day 30 and term. Labor onset is abrupt; delivery generally takes about 30 minutes. Dystocia is common. A fertile postpartum estrus occurs within 2-15 hours of parturition in about 80% of the sows. The average litter size is 3-4. The young are precocious at birth, being fully haired with eyelids and ears open, and teeth erupted. Birth weight is 60-100 grams. Young guinea pigs begin eating solid food during the first few days post partum. Weaning occurs at 14-28 days; weaning weight is 150-200 grams.
Newborn guinea pigs are sexed by examining the external genitalia.
Pseudopregnancy is uncommon.
Diseases of the Guinea Pig