Abstract
The maintenance energy requirement (MEm) of pregnant rats and net energetic efficiency for fetal growth during late pregnancy were examined by regression analysis. Pregnant rats, weighing about 180g, were fed on 20% casein diet during early-mid pregnancy and then divided into three groups-ad libitum-fed, 50% food restricted, or starved. A linear relation between the energy balance (Y, kcal/100g BW/day) and the metabolizable energy intake (X, kcal/100g BW/day) was obtained as Y=0.81X-14.8 3 (n: 17, r=+0.99, p<0.001). The X-intercept, MEm, was calculated to be 18.31 kcal/100g BW/day. Pregnant animals fed ad libitum retained 6.1 and 1.1 kcal of energy daily in their conceptuses and their own body, respectively, during late pregnancy. Assuming that the net efficiency of maternal energy deposition is equal to that for size-and age-matched nonpregnant rats, the net energetic efficiency for fetal growth was calculated to be 82%. This value was very close to the net efficiency for weanling rats reported previously, suggesting that the net energetic efficiency for maximum growth in well-nourished rats is about 82%.
