Repeated tests of intermale aggression in mice (Mus musculus) are influenced by housing and test conditions

Young adult male Binghamton Heterogenous (HET) mice were housed either individually or in groups of four, in two-tiered cages for 11 days before their agonistic behavior was observed. Pairs of male mice were tested 3 min each day for 9 consecutive days. Agonistic behavior was observed in two-tiered cages in which there were either clean pine shavings or shavings soiled by young adult female HET mice. Housing and shaving conditions interactively influenced aggression observed over the course of testing. That is, when individually housed mice were tested with clean shavings and when group-housed mice were tested with female-soiled shavings, agonistic behavior decreased over days, but when isolated mice were tested in soiled shavings and when group-housed mice were tested in clean shavings, aggression increased over the course of the 9-day test period.