Braden, G.C., Rasmussen, S., Tolwani, R.J. 2014. Effects of breeding configuration on behavior, reproduction, and pathology in the laboratory mouse (Mus musculus). American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 605. (Abstract #P210).

While numerous published studies have evaluated the effect of housing density on the wellbeing of laboratory mice, little is known on the effect of breeding configuration. The eighth edition of the Guide for the Care and Use of Laboratory Animals lists the recommended minimum floor area/animal for a female mouse and her litter as 51 in. Additional consideration is needed for other breeding configurations such that there is sufficient space for litters to develop to weaning without resulting in “detrimental effects for the mother or the litter.” For institutional housing density policies that deviate from the recommendations of the Guide, the 8th edition of the Guide encourages the use of performance indices to help determine appropriate space allocation. We present preliminary data studying the effects of 4 different breeding configurations (pair, trio with litter culled to ≤ 10, trio with nonculled litters, and harem) on environmental, behavioral, and pathologic changes in both C57BL/6 and BALB/c mice. Our hypothesis was that a pair breeding configuration is the least stressful for both the dam and litter. Additionally, we hypothesize that overcrowding will have a similar behavioral and pathologic effect as seen in mouse models of acute and chronic stress. We measured ammonia levels at the cage level, growth curves, and mothering behavior. A series of behavioral tests, including the elevated plus maze and tail suspension test (TST) were performed on weanling mice. Growth rates were slower in BALB/c harem-raised mice, however positive maternal behavior was most prevalent in the harem breeding configuration. Ammonia levels tended to be approximately 100 to 150 ppm over the latrine area by 7-d cage change interval, however, levels measured at the middle of the cage rarely reached > 50 ppm. Weanlings raised in harems tended to be immobile longer on the TST and there were no significant differences found on EPM. In summary, there appear to be both benefits and detriments to all examined breeding configurations.