Spontaneous Maternal Behavior of Laboratory Mice: Strain Differences

Hill, Elizabeth, and Sylvia Malcore

Maternal behavior of inbred laboratory mice has been shown to vary by strain, genetic mutation, and environmental conditions. Much less is known about the maternal motivation of virgin, nulliparous females. We tested nulliparous female mice during standardized pup retrieval tests, a 10-minute exposure to 2 foster pups, 3 days old. Two inbred strains of mice were tested, C57BL/6 and BALB/c. About half of the C57 mice (6/13) but only 2/15 BALB females retrieved at least one of the pups to the nest area during the test (chi-square=3.779, p=.052). Both pups were retrieved by 5 of 13 C57 and by 1 of 15 BALB (chi-square=4.425, p=.035). Most of the females engaged in nest-building (11/13 C57, 7/15 BALB; chi-square=4.608, p=.032), but hovering over pups was shown by fewer (2/13 C57, 5/15 BALB, n.s.). C57 females spent more time nest-building (p=.001), while BALB females spent more time licking and/or sniffing the pups (p=.002). In comparison, 4 experienced mothers (2 from each strain) retrieved both foster pups within 2 minutes and 3 of the 4 hovered over the pups for the remainder of the test. Spontaneous maternal behavior was more elaborately shown by the C57 females than those from the BALB strain. Future studies will investigate these differences in greater detail.