[Explanation and prediction of the kinetics of degradation in a Rusitec fermentor of nitrogenous vegetable matter after cell wall fractionation].

The relation between nitrogen solubility in Van Soest detergents and in vitro nitrogen degradation was studied on 11 substrates with degradation process calculations in digestive trials and an artificial semi-continuous flow (Rusitec) rumen. The kinetics of plant protein degradation in Rusitec, especially the maximum degradation values, were rather similar to those calculated from literature data obtained in situ. In the exponential model used to describe the protein degradation, the maximum disappearance (a + b) was negatively correlated with the percentage of acid detergent insoluble nitrogen in the Van Soest (ADIN/Total N). In the foods tested, the non degradable fraction corresponds to a quantity which is equivalent to approximately 76% of the ADIN fraction. The instantaneously degraded nitrogen (a) was rather well explained by the percentage of neutral detergent insoluble nitrogen in the Van Soest (NDIN/Total N). The rate of disappearance (c) of the slowly degraded fraction was inversely correlated with the proportion of ADF in the NDF, which demonstrates the latter's resistance to degradation. This type of fractionation could be used in predicting nitrogenous value of feed stuffs for ruminants.