Gaskill, B., Winnicker, C. L., Garner, J. P. et al. 2011. The naked truth: Breeding performance in outbred and inbred strains of nude mice with and without nesting material. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 741 (Abstract #PS95).

In laboratories, mice are housed at ambient temperatures between 20 to 24 °C, which is below their lower critical temperature of 30 °C, but comfortable for human workers. Thus, mice are thermally stressed, which can compromise many aspects of physiology from metabolism to pup growth. These effects may be exacerbated in the breeding of nude mice. We hypothesized that nesting material would allow nude mice to behaviorally thermoregulate, reducing heat loss to the environment. We predict this reduction will improve feed conversion as well as breeding performance. We housed naïve Crl:NU-Foxn1nu and CAnN. Cg-Foxn1nu/Crl breeding trios (2 haired females:1 nude male; 30 cages per strain) in shoebox cages at approximately 21 °C either with or without 8 g of nesting material for 6 mo within an isolator. Nest quality was scored weekly using a previously published standard scale. Feed was weighed when added and weighed back at the end of the experiment. At weekly cage changes fresh nesting treatment was provided. Reproductive observations were made 3 times a week and pups were weighed and sexed at weaning (21 to 28 d). Analyses used GLM with post hoc contrasts. Nesting material significantly increased the number of pups weaned per cage (F1,55 = 12.44; P < 0.001) by nearly 10 pups on average. The amount of feed needed to produce 1 g of weaned pup was almost halved when mice were provided nesting material (F1,55 = 8.5; P = 0.005). However, the total feed consumed by both treatments was not significantly different (F1,53 = 1.58; P = 0.21). The breeding index (pups weaned/female/week) was significantly higher when nesting material was provided (F1,55 = 10.15; P = 0.002). Thus, nests lessen the thermal impact of standardized cool temperatures on nude mice. However, the energy (using feed consumption as a proxy) conserved by nesting material is not simply freed up from heat generation but reallocated to improved breeding performance. Together these data show that good welfare is good business and good science.