Mise au point d'une méthode de laboratoire de prévision de la dégradabilité des protéines alimentaires des aliments concentrés dans le rumen

Abstract

The extent to which dietary proteins are absorbed in the small intestine of ruminants is dependent upon the amount and the rumen degradability of crude protein in the feed. The degradability of feeds nitrogen is calculated from kinetics of in sacco degradation, taking into account the rate of particle exit from the rumen as 0.06/hour. However, there are potentials for laboratory methods which are cheaper and more easily carried out. We propose a method based on nitrogen hydrolysis over 1 and 24 h with a bacterial protease in a borate-phosphate buffer maintained at pH 8. The enzymatic concentration (of Sigma type XIV), which was finally retained, was of 1 mg/50 ml of buffer added to a fixed quantity of substrate rather than to an iso-nitrogenous substrate. The effects of pH, the type of buffer used and of a pre-treatment were investigated. The prediction of theoretical degradability (DT) was more accurate when the Sigma type XIV enzyme was used as compared to the other enzymes which were tested : "protease Merck" and "Ficine" (table 2). This laboratory method (table 5), applied on 12 different feeds, enabled the prediction of DT to be made with more accuracy than when the usual method was used (i.e. solubility in a phosphate buffer at pH 6.9).