Changes in responsiveness to newborn pups in pregnant, nulliparous golden hamsters.

Virgin female hamsters were mated and tested once daily for maternal retrieving behavior beginning on days 0, 5, 9, 13, 15, of the 16 day gestation period to determine if responsiveness toward newborn pups changes as pregnancy proceeds. Upon initial exposure to 3 newborn pups, only a small percentage of early-to-mid-pregnant females exhibited maternal retrieving behavior spontaneously. In contrast, over half of the 15 day pregnant females displayed retrieving during the first test. Despite the high frequency of initial pup-directed aggression and cannibalism, maternal retrieval was induced in the majority of the females in all groups by repeated daily exposure to 3 newborn pups. However, no significant differences were observed in the number of pup exposure periods required to induce maternal retrieving in 0, 5, and 9 day pregnant females. It is concluded that the high level of maternal responsiveness observed in the parturient hamster develops somewhat abruptly during late pregnancy. In this respect, the pattern observed in the hamster differs from the more gradual increase in maternal responsiveness reported in mid-to-late-pregnant mice and rats.