Bret R. Tallent and Dr. Jonathan Lifshitz
In this project, funded by an AWI Refinement Grant, we tested whether raising male mice in partially divided cages affected aggression and behavioral performance from weaning through 180 days old in comparison to standard housing. Mice were weaned at 21 days old (Day 0) and randomly assigned to one of two groups: standard cage (Group 1) and cage with partial cage divider of corrugated plastic (Group 2). Each group contained five cages and each cage contained five mice. Animals underwent a battery of behavioral tasks beginning on Day 40 and finishing on Day 70. After resting for 42 days, animals were observed for seven consecutive hours on days 112, 116, 130, 131, 137, and 158. Cage environments were reversed on day 130 by removing dividers from Group 2 animals and adding dividers to Group 1 animals. Observers unaware of the study design and hypothesis scored each video for number and type of aggressive behaviors. During observation periods, animals were weighed and checked for bite wounds and had blood drawn for corticosterone levels (a measure of stress).
Body weight was statistically greater in mice housed with cage dividers compared to standard housing, which is indicative of healthier animals. Mice housed in partially divided cages had equivalent performance to those in standard housing on behavior tasks to evaluate neurological function, except for reduced anxiety in the elevated-plus maze. Bite wounds were fewer in partially divided cages than in standard cages. When dividers were added to long-established standard cages, the incidence of aggressive events and wounding subsided; when dividers were removed from long-established divided cages, no change in the incidence of aggressive events or wounding was noted. In sum, cage dividers may produce or preserve a hierarchy by providing the opportunity to exhibit submissive or escape behaviors. Compared to baseline, plasma corticosterone values were higher at cage change, but otherwise inconclusive.
Weaning mice directly into partially divided cages significantly reduced aggressive behavior and had persistent effects on behavior and physiology. In addition to reducing aggressive posturing, scuffling, and biting behaviors, cage dividers reduced anxiety in the elevated-plus maze, while not altering other standard neurological task responses. These data indicate animal welfare can benefit from the use of partial cage dividers.
Bret Tallent is the manager of the Phoenix Children’s Hospital Research Laboratory. Dr. Jonathan Lifshitz is an associate professor and director of the Translational Neurotrauma Research Program at the University of Arizona College of Medicine.