Modulation of aggression in male mice: influence of group size and cage size

Aggression in group-housed male mice is known to be influenced by both cage size and group size. However, the interdependency of these two parameters has not been studied yet. In this study, the level of aggression in groups of three, five, or eight male BALB/c mice housed in cages with a floor size of either 80 or 125 cm(2)/animal was estimated weekly after cage cleaning for a period of 14 weeks. Furthermore, urine corticosterone levels, food an d water intake, body weight, and number of wounds were measured weekly. At the end of the experiment, tyrosine hydroxylase (TH) activity, testosterone levels, and weight of spleen, thymus, testes, and seminal vesicles were de termined. Results indicate a moderate increase of intermale aggression in l arger cages when compared to the smaller cages. Aggression in soups of eigh t animals was considerably higher than in groups of three animals. The incr ease of agonistic behavior was observed both in dominant and subordinate an imals. Physiological parameters indicate differences in stress levels betwe en dominant and subordinate animals. It is concluded that aggressive behavi or in group-housed male BALB/c mice is best prevented by housing the animal s in small groups of three to five animals, while decreasing floor size per animal may be used as a temporary solution to decrease high levels of aggr ession in an existing social group. (C) 2001 Elsevier Science Inc. All righ ts reserved.