Some like it hot: Mouse temperature preferences in laboratory housing

In standard laboratory environments mice are housed at 20-24°C. However, their thermoneutral zone ranges between 26°C and 34°C. This challenge to homeostasis is by definition stressful, and could therefore affect many aspects of physiology and behavior. We tested the hypothesis that mice under standard laboratory conditions are not housed at a preferred temperature, and predicted that this would be evident in thermotaxis and other behavioral responses to ambient cage temperature. We assessed the temperature preferences of C57BL/6J mice in standard laboratory housing from 4 to 11 weeks of age. Forty-eight mice (24 male and 24 female in groups of three) all born on the same day were randomly assigned to one of eight age treatments. One cage of males and one cage of females were tested each consecutive week. Mice were tested in a set of three connected cages with each cage's temperature set using a water bath. On days 1-3 each group of mice was acclimated to each of the three temperatures (20°C, 25°C, or 30°C) in a random order. Then each group was given free access to all temperatures on days 4-6, and video taped continuously. The location of each mouse and the occurrence of three behavioral categories (Active, Inactive, and Maintenance) were recorded by instantaneous scan samples every 10min over the 3 days, and time budgets calculated. While both sexes chose warmer temperatures overall (P <0.001), they preferred warmer temperatures only for maintenance and inactive behavior (P <0.001). This effect was most pronounced in females (P =0.017). As temperature selection varied with time of day (P <0.001), these behavioral differences cannot be due to ambient temperature dictating behavior. We conclude that C57BL/6J mice at 20-24°C are not housed at their preferred temperature for all behaviors or genders, and that it may not be possible to select a single preferred temperature for all mice.