One of the problems often encountered with group-housed male mice is excessive aggression which can lead to negative affects both on the well-being of the animals and on the validity of experimental results. In order to minimize the risk of male aggressiveness, Envigo is housing male mice as cage mates from weaning onwards and will not mix these with unfamiliar mice upon shipping. Nevertheless mice can show aggressive behavior upon arrival and housing at the customers facility due to differences in husbandry and hierarchy. It is therefore advisable to not mix male mice from different delivery boxes and to house them in small groups (three to five animals per cage) as this will reduce the incidents of stressful situations.
While mice can be socially harmonious, there are times when they can display aggression. This applies to mice in nature or in captivity. When mice are group housed in the laboratory, aggression can be triggered which, up to a certain level, can be regarded as normal or natural. However, when aggressive interactions between cage mates cause severe injury and stress in the animals, it leads to negative effects both on the well-being of the animals (both dominant and subordinate) and on the validity of experimental results. Although mostly associated with males, females can also exhibit aggressive behavior.