Partial cage division significantly reduces aggressive behavior in male laboratory mice

Aggression in mice often results in injury leading to unplanned euthanasia or the initiation of protocols to isolate animals, thereby increasing research costs and straining resources. Here, we tested if adding a partial cage divider into existing mouse cages affected aggressive-like behavior in group-housed male mice (18 mice; 3 per cage). Mice were randomly assigned to one of two groups upon arrival to the vivarium: (1) standard cage; (2) cage with a partial cage divider. Behavioral observation over 12 hours were conducted at day one, two, and seven after receipt at the facility in order to assess aggression during the course of establishing dominance hierarchies. Observers blinded to study design and hypothesis scored each video for the number and type of aggressive behaviors, which were summed for each hour and analyzed. Results indicated a statistically significant decrease in aggressive behaviors of mice in cages with dividers compared to mice in standard cages. We conclude that cage dividers, which resemble burrows and provide access to common food/water, may promote rigorous research by reducing the number of animals used in a study and refining housing, thus, improving animal welfare.