Valuska, A. J., Mench, J. A. 2013. Size does matter: The effect of enclosure size on aggression and affiliation between female New Zealand White rabbits during mixing. Applied Animal Behaviour Science 149(1-4), 72-76.

Social enrichment is increasingly employed to improve the welfare of laboratory animals, including rabbits. However, the high levels of injurious aggression that can occur when unfamiliar adult rabbits are introduced to one another are a barrier to implementing social housing. One factor that could affect aggressive interaction is the size of the enclosure in which the animals are introduced, although this has never been tested in rabbits. We evaluated the aggressive and affiliative behavior of 11 pairs of unfamiliar adult female New Zealand White rabbits during 1-h trials. Using a balanced repeated measures design, pairs were tested in a smaller (Small) enclosure the size of a double cage (0.76 m × 1.22 m × 0.61 m) and a larger (Large) enclosure (1.22 m × 1.22 m × 0.61 m), both of which contained PVC barriers that allowed contact but prevented injury. There were no main effects of treatment or treatment order on aggressive or affiliative behavior, but there were significant interaction effects (P = 0.01). During their first trial, pairs tested in the Large enclosure showed higher levels (P = 0.07) of affiliative behavior (mean number = 37.6 ± 5.0) and lower levels (P = 0.02) of aggressive behavior (back-transformed mean number = 1.1) than pairs tested in the Small enclosure (20.7 ± 3.0 and 3.5, respectively). During their second trials, pairs behaved as they did during their first trial, resulting in the opposite pattern: significantly more aggressive behavior in the Large enclosure than the Small enclosure (P = 0.002). In total, there were 47 bites observed among does first introduced in the Small enclosure, as compared to only one in the pairs first introduced in the Large enclosure. Overall, these findings indicate that the Large enclosure was effective at reducing aggression when rabbits were unfamiliar to one another, but that behavior during a subsequent interaction was determined by prior experience rather than enclosure size. More research is needed to determine whether does’ short-term behavior in an experimental apparatus is predictive of long-term pair housing success.

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