The effect of the protein level of food on the energy maintenance requirement of growing rats on different feeding regimens

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Male Wistar rats were fed in the live weight range between 70 and 200 g in periods alternately for maintenance and weight gain (semi ad libitum). The diets contained 10, 40 and 70% crude protein, resp., the ambient temperature was 30 degrees C. In agreement with two previous experiments 2 different feed regimes were used. Whereas in the first growth phase (up to about 150 g live weight) the supply of protein was constant for each group, in the second growth phase the protein level was changed between the groups from one period to the other. The energy metabolism on the feeding level of maintenance was measured by indirect calorimetry. At both feeding regimes a dependence of energy maintenance requirement on the protein level of feeding was established. The differences in the maintenance requirement between the 10% and 70% protein level and in the first growth phase also between the 10% and 40% protein level corresponded on average to a growth phase the expected values of which result from the different efficiency of ATP synthesis in the oxidative degradation of nutrients. It follows that--in accordance with the previous findings--the feeding regime does not influence the ratio of energetic utilization of nutrients in the maintenance metabolism of growing rats under the experimental conditions used by us. Further the results of all our studies on the dependence of the energy maintenance requirement of growing rats on the nutrient composition are summarized. We conclude that a dependence on the protein-carbohydrate ratio of the diet according to the different efficiency of ATP synthesis in the protein and carbohydrate catabolism can be reproducibly established by our experimental methods only then, if more than 50% of the energy maintenance requirement are covered from protein energy.