Breaking up is hard to do: Does splitting cages of mice reduce aggression?

Injurious aggression in group housed male laboratory mice is a common welfare issue that can also negatively affect study outcomes. Often, one mouse in the cage appears unwounded, and the current standard practice is to remove this presumed aggressor. This procedure is not based on empirical evidence and may impede welfare by singly housing animals. We experimentally tested the hypothesis that the apparently uninjured mouse is indeed the...