Volume I - Section I - Introduction 
Page 1-21 
and groups of mice. In one study, female CD-I mice were housed in groups of five or 
individually in a temperature gradient while selected T a and motor activity were 
monitored. Single- and group-housed mice displayed a circadian oscillation of selected T a 
with relatively warm T a of ~29 °C selected during the daytime and cooler T a of ~ 25 °C 
during the night. Motor activity was low during the day and high at night. Selected T a of 
aged (11 month old) mice was ~1.0 °C warmer for single mice as compared to groups. 
Thermal preference of younger mice (two months old) was similar for individual- and 
group-housed animals. In another study, autonomic thermoregulatory requirements were 
measured in groups of female CD-I mice that were placed inside a direct calorimeter. 
Groups of five mice displayed a minimal metabolic rate at a T a of 30 °C. As T a decreased 
below 30 °C, metabolic rate increased in a near linear fashion. Thus, groups of five mice 
display a metabolic profile that is qualitatively similar to individual mice. Their zone of 
metabolic thermoneutrality is approximately 30 °C. Daytime metabolic rate has not been 
determined in groups of mice. The operative T a of mice housed in standard facilities was 
estimated by measuring the cooling rate of "phantom" mice modeled from aluminum 
cylinders. The results show that the typical housing conditions for single- and group- 
housed mice are much cooler than their T a for ideal thermal comfort. Wood shaving 
bedding material provides the best type of insulation that allows mice to maintain a 
relatively warm microenvironment. Wire-screen floors and wood chip bedding has 
minimal thermal insulative value. 
• To summarize, groups of five mice display a behavioral and autonomic thermoneutral 
zone that is surprisingly similar to individual mice. The standard housing T a of 22 to 
24 °C is significantly below the thermoneutral zone of groups of mice suggesting that 
they are subjected to varying degrees of cold stress under standard housing conditions. 
C. Yamauchi, S. Fujita, T. Obara, and T. Ueda: Effects of Room Temperature on Reproduction, 
Body and Organ Weights, Food and Water Intake, and Hematology in Mice, 1983, Exp. Anim., 
32:1-11. 
Two consecutive generations of mice were raised at graded room temperatures ranging 
from 12 to 32 °C at intervals of 2 °C. The delivery rate decreased at 30 and 32 °C, and the 
litter size and weaning rate decreased above 28 °C. No significant difference was 
demonstrated within the 12 to 26 °C range for any reproduction parameters observed. The 
body weights of the first-generation mice bom at 22 °C did not significantly differ after 
being transferred to rooms in the 14 to 28 °C range after eight and 16 weeks of exposure. 
The second-generation mice bom and reared at various temperature levels did not show 
significant intergroup differences in weight within the 20 to 26 °C range at any age in the 
growth period. No significant intergroup difference was observed within the 20 to 26 °C 
range with respect to food and water intakes in the second-generation mice. 
Hematological values and organ weights in the first- and second-generation mice of both 
sexes did not significantly differ in any parameter within the 20 to 26 °C range. The 
