Brown fat is also called the hibernating gland, although the rat does not hibernate. Nutrition Rats should be fed a commercial pelleted rat or rodent diet and water ad lib. These diets are nutritionally complete and do not require supplementation. Reproduction Breeding onset is between 65-100 days of age in both females and males, although females may have their first estrus at 35 days. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening.
Vaginal smears are useful for determining the stage of the estrous cycle.
The presence of sperm on a vaginal smear is a good indicator of mating. The Whitten effect, the synchronization of the estrous cycles of females exposed to the pheromones of a male occurs in rats, but is not as pronounced as in mice. The average gestation period is 22 days. A fertile postpartum estrus occurs within 48 hours of parturition, and simultaneous lactation and gestation may prolong gestation 3-5 days due to delayed implantation. The average litter size is 6-12.