Decline of maternal behavior in the virgin and lactating rat.

Sensitized virgins and postpartum lactating mothers, both exhibiting maternal behavior, were given donor litters that increased in age by 1 day, for 28 days, starting at the onset of maternal behavior. Each day females were tested for maternal behavior with pups 4-8 days old: Maternal care (i.e., nursing/crouching, retrieving, nest building and licking) and maternal withdrawal, rejection, and prevention of nursing were recorded. After the ninth day, females were also tested with the progressively older pups from 10 to 28 days of age with which they were living. Virgins and lactating mothers showed generally similar patterns of maternal care although some differences were found, and they declined in maternal behavior toward the older pups in a similar manner. Maternal behavior did not decline in tests with younger pups. The results are interpreted as supporting the hypothesis that the decline as well as the maintenance of maternal behavior postpartum is nonhormonally mediated.