Nutrient dependence of energy conservation requirements in rats. 4. The influence of protein levels of food on energy conservation requirements of rats during growth and after conclusion of the intensive growth phase

Albino rats bred in the institute (Wistar line) divided into 3 groups of 9 animals each received, beginning at the age of 4 weeks, feed mixtures with 10, 40 and 70% protein in the rations over a period of 24 weeks divided into 14 subperiods of study. The feed mixture changed cyclically for the groups of animals after each sub-period. Every period was divided into a growth period (8 days) with the rats kept in metabolism cages and a period of feeding on maintenance level (4 days) with the rats kept in respiration chambers. In both periods the temperature was kept constant at 30 degrees C. On 3 days of feeding on the maintenance level the metabolism parameters of energy, C and N metabolism were measured and energy maintenance requirement was ascertained. Both the energy maintenance requirement of the growing rats (up to 200 g live weight) and that of the nearly fully grown and fully grown rats resp. (greater than 200 g live weight) significantly depended on the nutrient composition of the feed mixtures supplied. It increased with the increasing protein and simultaneously decreasing carbohydrate quotas in the feed. On an average of the studies the rats had, in the sequence of 10, 40 and 70% protein content, an energy maintenance requirement of 383 +/- 31 (n = 105), 415 +/- 31 (n = 106) and 459 +/- 36 kJ metabolizable energy/kg LW0.75.d (n = 102). Energy maintenance requirement behaved relatively like 100:108:120. Based on the fact that energy maintenance requirement may be considered the requirement of ATP, relative expectancy values for energy maintenance requirement can be calculated with the energetic efficiency of the ATP synthesis (kJ metabolizable energy/Mol ATP gain) in nutrient catabolism from the relation of the experimentally ascertained nutrient metabolism at a variant supply of protein of 100:110:118. The hypothesis that the efficiency of ATP synthesis in the catabolism of the main nutrients supplying energy can be considered a relative measure of the dependence of the energy maintenance requirement on nutrient composition has been confirmed in this experiment. Different findings in earlier experiments raise the question if those findings were influenced by adaptation effects. An experimental solution of this question is considered important.