Do not use rabbit or guinea pig feed. Supplements of fresh vegetables, raisins, sunflower seed, etc., are unnecessary , and may be detrimental. Laboratory stocks are sexually mature by 55 days of age. The estrous cycle is five days. Gestation is 23 days, except in lactating females where it is delayed by 4-6 days to 28 or 30 days.
Breeding is optimized when animals are continuously retained in breeding pairs.
The females enter postpartum estrus about 12 hours after delivery and re-mate. Thus, serial litters are born at 28-30 day intervals. There may be a lag in breeding during midwinter under natural lighting. Peromyscus are bred in mated pairs. Each mating is assigned an individual identification consisting of a number with a letter prefix.