Degradation in the rumen of treated and untreated soya bean meal proteins

In order to estimate the quantity of solubilized nitrogen in the rumen that can contribute to intestinal feed non-ammonia nitrogen, degradation in the rumen was studied both for a control soya bean meal (cSBM) and a treated one (tSBM) to assess simultaneously the kinetics of: 1) protein disappearance from rumen bags and 2) rumen fluid contents in various nitrogen fractions in the rumen fluid: total nitrogen (Nt), ammonia nitrogen (NH3-N), non-ammonia nitrogen (NAN), peptides-N and amino acids-N, and true protein (protein-N). Measurements were taken on four sheep fed successiveIy with four diets consisting of hay plus one of the two meals, in the proportion of 40% and 20% control meal (cSBM 40% and cSBM 20%), 40% treated meal (tSBM) and a control diet based on hay alone supplemented with starch and urea (HSU). The effective degradability estimated with the nylon bag method was 0.727 and 0.502 for cSBM and tSBM, respectively. Sodium dodecyl sulphate gel electrophoresis (SDS-PAGE) showed that the cSBM conglycinins were degraded at a higher rate in the rumen than glycinins. The same proteins were degraded at a slower rate in the tSBM. Most of the nitrogen degraded in the rumen fluid was in NH3-N form, and only 30% as NAN. For cSBM, NAN comprised protein-N (concentration was low 1 and 2 h after feeding), peptides-N and amino acids-N, while for the treated meal the NAN comprised solely peptides-N and amino acids-N. These results showed that for soya bean meal - a feed in which the dietary proteins are strongly degraded at moderate rates - very little of the solubilized proteins from the bags can escape degradation in the rumen. Whatever the meal studied (treated or untreated), the estimation of feed NAN in rumen fluid able to escape degradation in the rumen compared to the degraded proteins (calculated from the degradation in nylon bags) was negligible (about 1%). ((C) Elsevier / Inra).