Attack by female mice on “Strangers”

In this study the aggressive responses directed by small groups of female mice towards virgin, pregnant, and lactating female strangers, which were individually introduced into their cages, were compared. The results obtained show that, except when lactating, pregnant females are neither attacked much more often nor any more severely than virgin mice. It is suggested that only the state of lactation favors the production of stimuli (olfactory) which release attack by female mice.