Aggression in group-housed laboratory mice: why can't we solve the problem?

Group housing is highly important for social animals. However, it can also give rise to aggression, one of the most serious welfare concerns in laboratory mouse husbandry. Severe fighting can lead to pain, injury and even death. In addition, working with animals that are severely socially stressed, wounded or singly-housed as a result of aggression may compromise scientific validity. Some general recommendations on how to minimize aggression exist, but the problem persists. Thus far, studies attempting to find solutions have mainly focused on social dominance and territorial behavior, but many other aspects of routine housing and husbandry that might influence aggressive behavior have been overlooked. The present way of housing laboratory mice is highly unnatural: mice are prevented from performing many species-typical behaviors and are routinely subjected to painful and aversive stimuli. Giving animals control over their environment is an important aspect of improving animal welfare and has been well-studied in the field of animal welfare science. How control over the environment influences aggression in laboratory mice, however, has not been closely examined. In this article, we challenge current ways of thinking and propose alternative perspectives that we hope will lead to an enhanced understanding of aggression in laboratory mice.