In general, veterinarians do not recommend that individual pet owners attempt to breed guinea pigs. It is often difficult to find homes with caring and responsible pet owners for young guinea pigs. Breeding often reduces the lifespan of female guinea pigs. Breeding a female guinea pig for the first time after she reaches 8 months of age can be very dangerous because of the normal stiffening of the pubic symphysis (a joint of tough fibrous cartilage between the 2 pubic bones of the pelvis) that occurs when the female reaches adulthood. Sows that reach adulthood without a prior pregnancy may not be able to deliver their young normally. Cesarean sections are rarely successful in guinea pigs even when performed by a veterinarian who has experience with guinea pigs.
Spaying or neutering of pet guinea pigs can be done by a veterinarian experienced in dealing with small animals, but the surgery can be expensive and does carry risks. Neutering a male is generally easier than spaying a female. However, guinea pigs often do not react well to surgery, anesthesia, or being kept in unfamiliar surroundings. The safest, easiest, and least expensive way to prevent breeding is to house male and female guinea pigs separately.
If you do decide to have your guinea pig spayed or neutered, seek out a veterinarian who has successfully done a large number of these surgeries. After the surgery, keep your pet quiet and separated from other guinea pigs while recovering. A small, clean cage with towels for bedding works well. The towels should be changed at least twice a day. Check to see that the guinea pig is eating and drinking; extra vitamin C may also be helpful.
Male guinea pigs (boars) usually mature sexually and can mate as young as 2-3 months of age. Female guinea pigs (sows) typically mature sexually at 2 months of age (55 to 70 days). However, both males and females can mature and be fertile even earlier. Females can have estrous or fertile periods at any time of the year, but they are most common in the spring. The estrous cycle length is 16 days. A female is fertile for about 6 to 11 hours, most often during night hours. Female guinea pigs begin a new estrous cycle shortly after giving birth.
The guinea pig gestation period is 59 to 72 days. The litter size ranges from 1 to 8 pups, but a litter of 2 to 4 is more common. A female can give birth to up to 5 litters per year. When a guinea pig is about to give birth, any male guinea pigs near her will gather around and try to become the dominant male in order to both protect the female and mate with her. The female has a short postpartum estrus that will last for only about half a day and, without a dominant male, all of the males will try to mate with the new mother.
Newborn guinea pigs weigh about 3.5 ounces (100 g). Even at such a small size, they have hair and are able to see and run. They will nurse from their mother but are able to nibble at solid food (such as moistened pellets) within 2 days. The mother has a single pair of mammary glands from which the newborns will nurse until about 3 weeks of age. When they reach about 6 ounces (170 g), the offspring will stop nursing and eat the same foods as their parents.
It is important to begin to carefully handle young guinea pigs when they are only 2 or 3 weeks old. This is the period when young guinea pigs will develop bonds with humans and learn to accept being held.