The single most important consideration regarding guinea pig breeding is that the female guinea pig (sow) should be bred between four and seven months of age if she is to be bred at all. The pelvis (birth canal) of the guinea pig fuses after seven months of age in the female guinea pig, thus preventing the babies from passing easily. Breeding a virgin sow after she is seven months old commonly results in very serious and often fatal problems with delivery. Males (boars) should be at least four months of age before breeding.


The sow’s estrous cycle lasts 14-19 days. The actual period in which the sow is receptive to the boar for breeding is approximately 8-15 hours during this cycle. Slows often return to “heat” within a few hours after giving birth. Pregnancy lasts between 63-70 days.


Pregnant sows exhibit a grossly enlarged abdomen during the later stages of pregnancy. An uncomplicated delivery usually takes about ½ hour with an average of five minutes between babies. Litter size range between one and six, with an average of three to four. Guinea pigs are well developed at birth. They weigh between 50 and 100 grams and have a full hair coat. Babies are even born with teeth and with their eyes opened.


Guinea pig young can eat solid food and drink from a bowl shortly after birth, but it is recommended to allow them to nurse for three weeks before weaning.