Effects of maternal state on the responsiveness to nest odors of hooded rats.

Two experiments were designed to determine if pregnant and lactating rats are differentially attracted to their own bedding at various stages of the reproductive cycle and whether they will discriminate between their own nest materials and those of virgins and other lactating animals. We found that from just before birth until the second week postpartum, rats are attracted to their own bedding but do not differentiate between their own and that of other maternal animals. It is suggested that the responsiveness to nest odors in prepartum pregnant animals is a result of hormonal events prior to parturition. In addition, early maternal activities are thought to be facilitated by changes in responsiveness to olfactory stimuli and also by the presence of an attractant which contributes to nest odors.