Effects of mother-litter separation and reunion on maternal aggression and pup mortality in lactating hamsters.

This study examined the effects of a 24 hr mother-litter separation on maternal aggression and pup mortality in hamsters. There were four lactating groups tested for aggression in their home cages on days 5 and 15 postpartum: a group that was separated from their litters for 24 hr, a group that was not separated from their litters and two 24 hr separation groups in which the litters were returned 30 and 120 min prior to the aggression test. Nonreceptive, estrous cycling animals were used as controls (tested twice, 10 days apart) and as intruders. Measures of aggression recorded during the 10 min tests included the number of attacks, fights, chases and intruder retreats. Pup mortality was examined in the 4 lactating groups and in two additional non-tested groups, one of which was separated from their litters for 24 hr. Lactating hamsters initiated significantly higher levels of aggression than control animals. Mother-litter separation (24 hr) significantly decreased levels of aggression and these levels were restored when litters were replaced 30 and 120 min prior to aggression tests. There were few differences in levels of aggression between days 5 and 15 of lactation. Pup mortality was significantly greater between days 5-6 and 15-16 of lactation among those groups that were separated from their litters compared to those groups that were not separated. Significantly higher mortality levels were found between days 7 and 15 of lactation among the 2 groups in which pups were returned prior to the aggression test compared to all other groups.