Influence of plane of nutrition on body composition, organ size and energy utilization of Sprague-Dawley rats.

Male (61) and female (53) Sprague-Dawley rats (31 d of age, 85 g) were used to evaluate the influence of plane of nutrition on body composition, internal organ size and energy utilization. Six male and nine female rats were sacrificed initially. The remaining animals were randomly assigned, within sex, and fed to gain either 105 g (H) or 40 g (M) or lose 25 g (L) during a 21-d period. Nine rats each from the H and M groups and six from the L group were then sacrificed. The remaining rats from the H (27) and M (27) groups were fed to gain at the H, M or L rate and rats from the L (12) group were fed to gain at the H or M level during a second 21-d period. All rats were sacrificed at the end of the second period. Body composition and weights of internal organs were determined and relationships between energy intake and energy gain were evaluated. Results indicated that at the end of period 2, body composition at equal age and body weight was influenced by nutritional treatment. At equal body weight, body protein weights were lower (P less than 0.05) and body fat, liver and gut weights higher (P less than 0.05) for rats on higher planes of nutrition. Feed required for maintenance of rats during period 2 tended to be lower and efficiencies of gain tended to be higher for rats fed the low level than for those fed the high level during period 1. Rats fed the medium level during period 1 had similar maintenance requirements but higher efficiencies of gain during period 2 than rats fed the high level during period 1. These results suggest that previous nutrition influenced energy utilization through adaptation of high energy expending internal organs as well as through alterations in body composition and composition of body weight gain.