Comparison of control diets containing various protein levels for determining net protein utilization by rats.

The objective of this study was to explore the commonly used method of Miller and Bender for determination of the net protein utilization (NPU). Eight test diets of different protein quality from both animal and vegetable sources were studied at 10% protein level with the protein content of the control diets being 0, 1, 2, 3 or 4% whole egg protein. At the end of the 10-d feeding period body nitrogen of the rat carcasses (test and control groups) was analyzed. Comparison of the body weight was also made. Rats fed either 2 or 3% egg protein maintained initial body weight and body nitrogen at the end of the feeding period. The absence of a significant difference between the NPU values of the test proteins calculated with the 1, 2, 3 or 4% egg protein group as the control and the NPU values obtained by the method of Miller and Bender (which uses the protein-free group as the control) demonstrated that the relative nutritive value for different proteins could be correctly determined by the traditional NPU method.