Food consumption and body composition in mice selected for high wheel-running activity

The effects of genetic selection for high wheel running (13th generation) a nd prolonged access (8 weeks) to running wheels on food consumption and bod y composition were studied in house mice (Mus domesticus). Mice from four r eplicate lines selected for high wheel-running activity ran over twice as m any revolutions per day on activity wheels as did mice from four replicate control lines. At approximately 49 days of age, all mice were placed indivi dually in cages with access to wheels and monitored for 6 days, after which wheels were prevented from rotating for the "sedentary" individuals. Durin g the experiment, five feeding trials were conducted and body mass was meas ured weekly. After 8 weeks, body composition was measured by hydrogen isoto pe dilution. Across the five feeding trials, mice in the "active" group (wh eels free to rotate) consumed 22.4% more rood than mice in the "sedentary" group (wheels locked); mice from the selected lines consumed 8.4% more food than mice from the control lines (average of all trials; body mass-correct ed values). In females, but not males, we found a significant interaction b etween selection and wheel access treatments: within the "active" group the difference in food consumption between selected and control animals was gr eater than in the "sedentary" group. At the end of the study, mice from the "active" and "sedentary" groups did not differ significantly in body mass; however, mice from the selected lines were approximately 6% smaller in bod y mass. Estimated lean body mass did not differ significantly either betwee n selected and control lines or between wheel-access groups (P > 0.3). Mice from selected lines had lower total body fat compared to mice from control lines (P = 0.05, 24.5% reduction; LSMEANS) as did mice from the "active" c ompared to "sedentary" group (P = 0.03, 29.2% reduction, LSMEANS). Under th ese conditions, a sufficient explanation for the difference in body mass be tween the selected and control lines was the difference in fat content.