Improvement of the Procedure to Determine Gross Protein Value with Growing Chicks

Abstract

More stable linear relationship was observed in the relationship between logarithm of dietary protein level and body weight gain of chicks per 100g feed than that between dietary protein level itself and body weight gain. Based on this finding, gross protein value of casein and a protein mixture of 89.6% soybean meal, 10% fish meal an 0.4% DL-methionine were estimated as slope ratio of two log dose-response lines in 23 experiments, among which linear protein level-response lines were observed only in 6 experiments. A casein-amino acid mixture, composed of 90.9% casein, 5.4%L-arginine•HCl, 1.7% DL-methionine and 2% glycine, was used as standard protein.Gross protein value of casein was 85 with 95% fiducial interval from 90 to 80. Gross protein values in literature, which were estimated using casein as standard protein, can be changed to new gross protein value based on casein-amino acid mixture as standard protein by multiplying the old value by 0.85.Gross protein value of the protein mixture was 102 with 95% fiducial interval from 107 to 98. The mixture can be used as auxiliary standard protein.New standrard procedure to estimate gross protein value is recommended, which is 5-point slope ratio assay, and by which gross protein value can be estimated in 6-day assay with about 540g or less of test protein.