Niu, Y., Zhang, M., Liu, J. 2011. The effect of cage enrichment on fluctuating asymmetry and fecal corticosterone of group-housed laboratory mice. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 740 (Abstract #PS91).

Fluctuating asymmetry (FA) represents small, random deviations from symmetry in bilaterally symmetrical anatomic characteristics, is highly correlated with the amount of stress during development, and thus, is considered as a potential welfare indicator. In the present study, female BALB/c mice were group housed (3 to 4 mice per cage) from 3 to 13 wk of age in standard or enriched cages provided with kraft paper tubes. Body weight gain of each mouse was monitored, and no significant difference between the standard and the enriched groups was found. Three recommended traits in living mice, the width of the carpal bone, the width of the joint between the third metatarsal bone and the digital bone on the hind paw, and the length of the incisor tooth at the top from the gum, were measured at 4, 7, 10, and 13 wk of age for assessing FA. Two traits based on fleshed bones, the length of mandibular bone between the dens incisive and the processus angularis, and the length of femur, were measured at the end of experiment. FA based on the data from living mice decreased over the 9 wk in enriched cages, while for the standard housed mice, FA were fluctuating or increasing. Significant lower FA values were also detected in the 2 skeleton traits of enriched mice. The levels of corticosterone in fecal samples were examined at the end of experiment, and mice in cages with paper tubes have lower levels of corticosterone when compared with those without enrichment (t = 4.715, P < 0.05). The lower corticosterone levels were consistent with the FA measurements in mice housed in enriched cages. These indicate that housing mice in group with enrichment is much more valid to decrease the environmental stress and improve welfare. Our findings also suggest that welfare can be markedly improved by simple cage enrichment using economical materials.