The ambient temperature (T-a) to house and study laboratory rodents is crit
ical for nearly all biomedical studies. The ideal T-a for housing rodents a
nd other animals should be based on their thermoregulatory requirements. Ho
wever, fundamental information on the behavioral thermoregulatory responses
of single- and group-housed rodents is meager. To address this issue, ther
moregulatory behavior was assessed in individual and groups of CD-1 mice ho
used in a temperature gradient. Mice were housed in groups of five or indiv
idually while selected T-a and motor activity were monitored. Single- and g
roup-housed mice displayed a circadian oscillation of selected T-a and moto
r activity with relatively warm T(a)s Of similar to 29 degrees C selected d
uring the light phase; during the dark phase selected T-a was reduced by 4
degrees C, whereas motor activity increased. Selected T, of aged (11 months
old) mice housed individually was similar to 1.0 degrees C warmer than the
group-housed mice. Thermal preference of younger mice (2 months old) was s
imilar for single- and group-housed animals. The operative T-a of mice hous
ed in standard facilities was estimated by measuring the cooling rate of "p
hantom" mice modeled from aluminum cylinders. The results show that the typ
ical housing conditions for single- and group-housed mice are cooler than t
heir T-a for ideal thermal comfort. (C) 1998 Elsevier Science Inc.