Body Composition at Vaginal Opening in Mice as Influenced by Food Intake and Photoperiod: Tests of Critical Body Weight and Composition Hypotheses for Puberty Onset

To determine if photoperiod and food intake influenced age and body composition at vaginal opening (VO), 80 mice were exposed to either 18L:6D (LL) or 6L:18D (SL) and fed either 3.64 g/mouse per day (HIGH) or 2.73 g/mouse per day (LOW) of Wayne Lab-Blox. Treatments began at weaning (21 to 23 days of age). Mice were killed at VO and analyzed for fat, water and protein content. Mice fed the HIGH ration were younger (P<0.01; 35.9 vs. 41.1 days) and heavier (P<0.001; 17.8 vs. 15.4 g) at VO than mice fed the LOW ration. Neither age nor weight at VO were affected by photoperiod. Fat content at VO was greater (P<0.001) for HIGH than LOW. Differences in fat percentage at VO between diet groups were greater for LL (9.7 vs. 7.0%) than for SL (9.1 vs. 8.6%), resulting in a photoperiod × ration interaction (P<0.01). Percent water and protein at VO were not significantly affected by photoperiod or diet. Within-group correlations between body weight and age at VO were not significant. Body water/body weight was inversely proportional to age at VO. This resulted from increased fat deposition in older animals of the LL-LOW group and increased percent protein in older animals of other groups. We concluded that dietary intake did not influence age at VO by affecting age at which a critical body weight or fat content were attained. A photoperiod of 18L:6D did not affect age at VO relative to 6L:18D.