Performance of mouse lines divergently selected for heat loss when exposed to different environmental temperatures. II. Feed intake, growth, fatness, and body organs.

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for feed intake, growth, body fatness, and organ weights when reared at 12, 22, and 31 degrees C, and investigate potential line x environment interactions. Feed intake was recorded weekly from 3 to 9 wk of age, and BW at 3, 6, and 9 wk of age. Body fat percent and organ weights were measured at 9 wk of age. No line x environment interactions were detected for any of the traits measured. The MH mice consumed more feed than ML mice from 5 to 9 wk of age. Between 8 and 9 wk of age, MH mice consumed 13% more feed than the ML mice, but they were relatively leaner (14.45 vs. 16.32% body fat); MC mice were intermediate for both traits. Mice in the cold environment consumed the greatest amount of feed, and those in the hot environment consumed the least. Males consumed more feed than females, and the difference was greater in the cold than in the hot environment. No differences in BW were found between the lines. Mice in the 22 degrees C environment were heavier than their age-matched counterparts in the other two environments, and males were heavier than females at all ages. Relative to BW, the three lines had similar tail length, body length, and liver weight. Mice in the cold environment had heavier spleens and livers than those in the hot environment but relatively shorter bodies and tails; the normal environment was intermediate for these traits. Results from this study indicate that selection to decrease maintenance requirements did not produce mice with any less ability to grow and perform under an array of environmental temperatures.