Social conflict reduction program for male mice.

Aggression within caged groups of unfamiliar male mice can be a serious welfare problem for maintaining mice in the laboratory. At our Center, two observation periods were set aside daily in order to identify, according to previously described behaviors, dominant mice and separate these when indicated. By reducing or eliminating the number of aggressive acts between group members in the same cage, our social conflict reduction program has led to a 57% reduction of mice being reported for clinical signs, death, and euthanasia. Welfare concerns seemed to be addressed. Therefore the program we implemented to reduce social conflict was effective in decreasing injuries and loss due to fighting. Minimizing aggression will have the additional benefit of reducing the confounding effect of stress on an animal's performance in experimental situations. This simple yet humane program can be applied easily to other animal facilities where male Crl:CD-1 mice (and possibly other stocks or strains) are used and fighting is a concern.