Guinea Pig Breeding

The sex of the mature guinea pig can be determined by observing the area of the lower body openings while pressing down gently on the animal’s abdomen just above the lower body openings. In the male, the genitals will appear. In the female only the body openings will be visible.
Each boar can be placed with from one to six sows; three or four sows is the optimum number for most males.
No special preparations are needed other than that the guinea pigs should be in good health and have a good diet, particularly of greens. Lack of greens and vitamin C will cause infertility, early abortion, reduced litter sizes and stunted growth. The cages should be of sizes discussed earlier.
Long-haired guinea pigs should be kept clipped, especially around the hindquarters; otherwise the coat will interfere with the nursing of the young.
Sexual maturity is reached at about five or six weeks of age, though sows should not be bred until they are about five or six months old. Breeding at this later age is less of a strain on the sow and the litters are usually stronger and more robust.
The female guinea pig’s estrus cycle runs from fourteen to seventeen days, with an average of about sixteen days and is repeated continually until pregnancy occurs. There may be some pauses in the cycle during the late winter months. The sow is willing to mate for one day during each cycle. This mating time, called estrus (or heat), occurs early in the cycle, on about the second day.
Pregnancy or gestation runs from fifty-nine to seventy-two days with an average of sixty-three.