The Determination of the Net Utilization of Proteins by a Shortened Method

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Abstract
A method is described whereby 7 proteins can be tested simultaneously in 10 days in 32 rats, with no N analyses other than on the food. Of 8 groups of 4 uniform rats each, one group was fed a non-protein diet, and each of the remaining 7 groups a separate test-protein diet for 10 days. At the end of the period the uneaten food was dried at 105[degree] and weighed, and the food consumed (and hence N intake) calculated. The animals were then killed with chloroform, and their body water determined. Body N was calculated from body water content and net protein utilization (NPU) by use of the equation: NPU = Body N of test group - Body N of non-protein group + N consumed by non-protein group divided by N consumed by test group. NPU values determined for 26 proteins showed good agreement with values reported in the literature. Biological value can be calculated by dividing NPU by digestibility. Estimation of the limiting amino acid in a given protein may be made by supplementing the protein with triads of the 9 amino acids essential for the adult rat.