Effect of predator exposure upon early pregnancy in mice.

Female CD-1 and C57 mice were inseminated according to standard procedures and randomly assigned to varied treatments in the first trimester of pregnancy. In the first experiment, mice housed for one week with preselected nonassaultive rats produced very few litters in contrast to controls. In the second experiment, this same effect was observed when inseminated mice were separated from the rat by a wire grid. In the third experiment, inseminated mice were exposed daily to saline or the urine of male or female rats in their home cage bedding. Fewer females exposed to rat urine of either sex produced litters.