Mirrors as potential environmental enrichment for individually housed laboratory mice

Abstract

Mirrors have been suggested as a potential environmental enrichment for animals that are individually housed. The present study examined the influence of a mirror on the behaviour of individually housed laboratory mice. Sixteen mice were placed into apparatus comprised of two preference cages connected by a tunnel. A mirror was placed in one of the preference cages (mirror) but not in the other (non-mirror) and the position swapped daily for 4 days. Thirteen of the 16 mice spent less time in the mirror cage than the non-mirror cage (Sign test; P=0.021) indicating an aversion to the mirror, however, the difference in occupation of the cages was not great. Overall, the mice occupied the mirror cage 47.6±4.7% of the time and the non-mirror cage 52.4±4.7%. There was no significant effect of the mirror on the number of mice building a nest in the mirror ( N=10) or the non-mirror cage ( N=6). The presence of the mirror significantly reduced feeding from the immediately adjacent feeder. The number of bouts, total time, and the mean feeding bout duration were all decreased by approximately 50–60% (ANOVA; P<0.05). Overall, these results show that a mirror is slightly aversive to individually housed mice during general cage occupancy, and more highly aversive during feeding. These data therefore indicate that in contrast to some other species, mirrors are probably not a suitable environmental enrichment for individually housed laboratory mice.