[Energy maintenance requirement and energy requirement for protein retention in growing rats and broilers. 3. Energy requirement for protein retention in rats].

In 4 experiments with 3 X 3 male Wistar rats each, which received rations with different protein content on 3 levels (10-40%), a total of 240 measurings of the total metabolism with the purpose of ascertaining the energy requirement for protein retention were carried out under the conditions of ad libitum feeding in the growth range between approximately 65 and 200 g live weight at a temperature of the environment of 30 degrees C. With 25% crude protein (caseine supplemented with methionine) in the feed mixture, with an energy content of the ration between 18 and 20 kJ/kg dry matter, the N-retention capacity of the animals was largely exhausted. When 150 g live weight were exceeded, the N-retention capacity of the animals decreased considerably. Energy retention in % of gross energy depended on the protein level of the feed rations; in all 4 experiments the rats achieved the highest energy retention with 10% crude protein in the feed. The level of energy utilisation decreased with the increasing protein content of the feed mixture. Requirement values of metabolisable energy per 1 J protein energy retention of 1.69; 1.93; 1.81 and 1.74 J were derived by means of multiple regression analysis for all 4 experiments, assuming the exponent 0.75 for the variable metabolic body size. The application of multiple regression analysis to the values of energy retention measuring in all 4 experiments results in the mean energy requirement of 1.67 J/J protein retention, which completely coincides with previous investigations. When the exponent 0.67 was assumed for the variable metabolic body size, the energy requirement data for the individual experiments resp. after the joint evaluation of all 4 experiments were 1.56; 1.75; 1.68 and 1.56; 1.53 J/J resp. The significant influence of the live weight, the consumption quota of digested nitrogen (protein level of feeding) and the protein retention quota on the value of protein requirement for protein retention was proved. This evidence is discussed with respect to further research for the factorial assessment of the bioenergetic of protein retention.