[Can a mouse be the object of maternal aggression on the part of a rat?].

It has been found that mice do not evoke interspecies maternal aggression in lactating female rats even if the latter kill little rats of their litter. Putting mice in cages with rats bearing for the first time, and their progeny for 24 hours after labor, increases the frequency of infanticide and progeny leaving by female rats. The infanticide by lactating rats towards their own litter does not depend on whether these females exhibit muricid or not. Putting mice in cages with rats 3-6 days before bearing for the first time or during 24 hours after labor by repeatedly bearing rats does not influence the frequency of progeny leaving and infanticide reactions of female rats.