The effects of cage cleaning on aggression within groups of male laboratory mice

Abstract

Cage cleaning is an unavoidable but frequent source of disturbance for mice maintained in the laboratory. A series of tests was conducted to assess how physical disturbance, the removal of odour cues and exposure to the odours of strangers experienced during cage cleaning affects aggression within established groups of male CFLP mice, Mus musculus. Handling mice decreased the latency to attack and increased the frequency and duration of aggression within groups. Transferring mice into completely clean cages reduced aggression compared to those replaced in home cages that had not been cleaned. Exposure to the odours of strangers while males were held temporarily in a handling bin had no significant effect on aggression when the males were transferred to clean cages or returned to their home cages. Aggression was greatest when mice were replaced in home cages that had not been cleaned but that had a clean sawdust substrate, and decreased with increasing removal of home cage odours on the cage base and grill. Common cage-cleaning practices in which only the substrate and parts of the cage are cleaned, and other procedures that involve daytime handling and replacing mice in their home cage may thus promote aggression within male groups. Transferring mice into completely clean cages is recommended when aggression within caged groups of males is a concern.