Protein quality of feeding-stuffs

1. Twelve commercial samples of high-protein feeding-stuffs, six of them fish meals, were used for a study of the reproducibility of chemical, microbiological and biological assay values for individual amino acids. Comparisons were also made of results obtained by different methods for the same amino acid. 2. For lysine there was quite good agreement between the results from the different laboratory tests for ‘available’ lysine. The values for ‘total’ lysine were, on average, 10 % higher than those for ‘available’ lysine. 3. For methionine the correlations between the chick assay and each of the laboratory tests were similar. 4. The results from the ‘total protein efficiency’ test of over-all protein quality, using chicks, showed a close correlation with the results of lysine or methionine assays according to which of the two amino acids was most deficient. 5. The results with tryptophan were difficult to interpret and no recommendations could be made as to procedures suitable for general use. 6. Although most of the present samples proved to be of good quality, only screening of a much larger number of samples will reveal to what extent commercial protein concentrates of low availability are still liable to come onto the market.