Abstract
In order to examine the susceptibility to postruminal digestion of feed protein which bypassed the rumen against an active proteolysis in it, artificial digestion studies using pepsin and pancreatin (P-P) were done with proteins of white fish meal (WFM), corn gluten meal (CGM), soybean meal (SBM), dehydrated alfalfa meal (DAM) and corn (CN) after the incubation for 0, 8 and 24 hours in the rumen of a cow by a nylon bag-method. After the digestion with P-P in vitro, P-P-digestible N-fraction was further divided into 5% sulfosalicylic acid (SSA)-soluble and-insoluble fractions. In the results, digestibilities calculated from P-P-soluble N/total N×100 showed a tendency to decrease slightly in SBM and DAM, but were almost constant in WFM, and even increased in CGM and CN with incubation time. On the other hand, digestibilities calculated from SSA-soluble N/total N×100 were almost unchanged in WFM, CGM and DAM, but were apparently increased in SBM and CN by incubation in the rumen. Any consistent relationship was not detected between the degradability of protein in the rumen and the in vitro digestibility with P-P. For instance, the digestibility of protein in WFM was relatively higher in spite of its lower degradablity in the rumen, and, on the other hand, the in vitro digestibility of protein in CN and DAM, which was degraded to a relatively greater extent in the rumen, was similar to or even lower than that of protein in CGM that was lowest in digestibility with P-P among five feeds. By incubation in the rumen, not only P-P-digestible N-fraction but also the indigestible N-fraction decreased at the same time except WFM. These results suggest that there is no relationship between the susceptibility to degradation of feed protein in the rumen and the susceptibility to post-ruminal digestion of the rumen-bypassed protein. It is considered that the cause will be attributed to difference in the specificity of substrate between the proteases functioning in the rumen and those contained in the gastric and pancreatic juice.
