Guinea Pig - Breeding

Breeding

The guinea pig is able to breed year-round, with birth peaks usually coming in the spring; as many as five litters can be produced per year. The gestation period lasts from 59–72 days, with an average of 63–68 days. Because of the long gestation period and the large size of the pups, pregnant females may become large and eggplant-shaped, although the change in size and shape varies. Unlike the offspring of most other rodents, which are altricial at birth, newborn pups are well-developed with hair, teeth, claws, and partial eyesight; they are immediately mobile, and begin eating solid food immediately, though they continue to suckle. Litters yield 1–6 pups, with an average of three; the largest recorded litter size is 17.

In smaller litters, difficulties may occur during labour due to over-sized pups. Large litters result in higher incidences of stillbirth, but because the pups are delivered at an advanced stage of development, lack of access to the mother's milk has little effect on the mortality rate of newborns. Cohabitating females assist in mothering duties if lactating.

Male and female guinea pigs do not differ in external appearance apart from general size. The position of the anus is very close to the genitals in both sexes. Female genitals are distinguished by a Y-shaped configuration formed from a vulvar flap; while the male genitals may look similar with the penis and anus forming a like shape, the penis will protrude if pressure is applied to the surrounding hair. The male's testes may also be visible externally from scrotal swelling.

Males reach sexual maturity at 3–5 weeks; females can be fertile as early as four weeks and can carry litters before they are adults. Females that have never given birth may develop irreversible fusing of the pubic symphysis, a joint in the pelvis, due to calcification which may occur between 6 and 10 months of age. If they become pregnant after this has happened, the birth canal will not widen sufficiently; this may lead to dystocia and death as they attempt to give birth. Calcification of the female's pubic symphysis (if not bred) is a common myth. The reason for potential calcification is an Metabolic disease, like Ochronosis. An healthy, normal female guinea pig's pubic symphysis does not calcify. Females can become pregnant 6–48 hours after giving birth, but it is not healthy for a female to be thus constantly pregnant.

Toxemia of pregnancy is common and kills many pregnant females. Signs of toxemia include anorexia, lack of energy, excessive salivation, a sweet or fruity breath odor due to ketones, and seizures in advanced cases. Pregnancy toxemia appears to be most common in hot climates. Other serious complications of pregnancy can include a prolapsed uterus, hypocalcaemia, and mastitis.