Effects of pregnancy and mating age on protein and fat deposition in polygenic obese mice.

Effects of pregnancy and mating age on rate (gain/day) and efficiency (gain/feed) of lean and fat deposition were determined in the M 16 line of mice selected for rapid postweaning weight gain. Correlated responses in M16 mice included increased lean and fat gain and efficiency. Exclusive of their litters, M 16 females had greater (P<.01) lean tissue growth and efficiency during pregnancy than M 16 virgin female contemporaries. Gain and efficiency of lean during pregnancy were higher (P<.01) in females mated at an early age (28.7+.5 days) than those mated at a normally later age (52.7_+.5 days). Pregnant females had decreased (P<.01) fat and energy retention and efficiency when compared with virgin controls of similar age. Early-pregnant females gained body fat and energy during pregnancy, whereas normalpregnant females showed a loss of body fat and energy. Total (female + litter) gain and efficiency of lean, fat and energy were higher (P<.01) in early-pregnant than normal-pregnant females. Total lean gain and efficiency were higher (P<.01) in gestating than virgin controls, but total fat and energy gain and efficiency were less (P<.01). During a 3-week postpartum test period, earlypregnant females did not differ from virgin controls in lean gain and efficiency, whereas normal-pregnant females were lower (P<.0 I) than virgin controls. Early-pregnant and normalpregnant females had higher (P<.01) fat and energy gain and efficiency than virgins during the 3-week postpartum period. (