PREDICTING INSITU DEGRADABILITY OF FEED PROTEINS IN THE RUMEN BY 2 LABORATORY METHODS (SOLUBILITY AND ENZYMATIC DEGRADATION)

Two techniques were investigated to find a laboratory method for the prediction of the in situ nitrogen degradation of concentrated feeds: a method using solubility in a buffer (phosphate buffer at pH 6.9) and an enzymatic technique (hydrolysis after 1 h (DE1) and after 24 h (DE24) by a protease extracted from Streptomyces griseus in a borate-phosphate buffer at pH 8). Ninety-seven samples of concentrated feeds, representing 26 single feeds and 49 commercial feed mixtures, were studied. Both methods allowed the same precision (residual standard deviation (RSD) approximately 0.030) if the 26 single feeds were grouped in classes. In contrast, for feed mixtures, the prediction was very precise and much better with the enzymatic method (RSD = 0.025) than with the solibility method (RSD = 0.049). In the French digestible proteins in the intestine (PDI) system, the enzymatic method is used as a laboratory method for nitrogen evaluation.