Guinea pigs have a relatively long gestation compared to other small mammals. The duration of pregnancy is 60 to 70 days, because of this guinea pigs give birth to well developed young. Guinea pig newborns are fully covered with hair, have open eyes and ears and have teeth present. This is of benefit to them as prey animals, and it allows them to be able to escape predators. However, it also means that guinea pig babies are quite large.
Despite guinea pig babies being 'large', the birthing process is often straightforward if the mother guinea pig has not experienced the fusing of the pelvic canal. As female guinea pigs age, their pelvic canal fuses to form a complete boney bridge. The fusion occurs around 8 months. If parturition (birth) occurs before this fusion takes place, the pelvic canal is able to relax and stretch in response to hormone secretions which makes the birthing process easier.
Guinea pigs show very few signs of imminent birth. Their behaviour doesn't discernably change and they do not make nests. The birthing process is also very fast. It is usually complete within 30 mins. It is for these reasons that owners will usually just find babies and not be witness to the birthing process. It is normal behaviour for the mother guinea pig to clean their newborn babies and lick them to stimulate the young guinea pigs to urinate/defaecate. Pregnant sows can get diseases associated with pregnancy. The risk of these diseases increases if the guinea pig is overweight. Pregnant sows still require a diet that is predominantly hay and room to exercise. Two diseases occurring during pregnancy or immediately after birth include pregnancy toxaemia and hypocalcaemia.
Both diseases have similar clinical signs which include depression, loss of appetite and muscle tremors. Pregnancy toxaemia tends to occur in the last 2 weeks of pregnancy or the first 2 weeks after birth. It is caused by the energy requirements of the sow outweighing her food consumption. This results in her breaking down fat reserves which leads to toxin release. Hypocalcaemia occurs when the dietary provision of calcium is insufficient for the increased demand for calcium to form the feotal skeleton and for lactation. In the late stages of pregnancy the sow may consume up to 3 times her usual intake of food. It is important in this time period to have easy access to food and water, not to restrict dietary calcium and to supplement with vitamin C. Newborn guinea pigs weigh between 50 and 100g. They are born with fur and teeth and can walk almost immediately. The sow does not seek out her young to feed but will allow them to suckle. Guinea pigs have two nipples and it is most important for them to suckle in the first three days. The young guinea pigs will start to nibble on solid food from day 2 and are weaned at 3 weeks. If the pup is orphaned, it will need bottle feeding and it is possible to have them on a completely solid diet from day 5.