Prenatal effects of parity on behavioral ontogeny in mice

In mice, parity and previous experience with pups may influence a mother's behavior towards her pups, thus possibly causing postnatal maternal effects on the subsequent development of the pups. The present experiment addressed the question whether parity also might have prenatal effects. We studied 622 pups from second or third litters that originated from 25 genetically different populations and had been fostered to random-bred lactating females. Development of responses was significantly delayed in mice from third litters, when compared to pups from second litters in three out of five sensorial and four out of eight motor tests. In addition, pups from second litters initially were slightly heavier than those from third litters. This difference in body weight disappeared after the 10th day postnatally. However, it should be noted that effect sizes were quite small.