In Situ Degradability of Protein and Dry Matter from Single Protein Sources and from a Total Diet

Abstract

The objective of this study was to determine dry matter (DM) and crude protein (CP) degradation of barley (B), canola meal (CM), soybean meal (SBM), meat and bone meal (MBM); and each of six total diets containing one of these protein sources. Six pregnant Holstein heifers fitted with permanent ruminal and duodenal cannulae were assigned in a 6 × 6 Latin square to the six dietary treatments. The six diets were formulated to provide different levels of CP in the diet dry matter: B, 14% CP; CM, 16.5% CP; SBM, 16.5% CP; MBM, 16.5% CP; CM, 19% CP; SBM, 19% CP. The effective degradability of DM and the effective degradability of CP were determined using an in situ nylon bag technique for the protein source alone and for each total diet. A ruminal outflow rate of .05/h was assumed. The effective degradability of DM for the protein sources were 74.1, 63.0, 66.6, 39.0, 64.2 and 69.4, and for total diet: 60.7, 59.2, 59.9, 55.8, 59.3 and 61.4 for B14, CM16.5, SBM16.5, MBM16.5, CM19 and SBM19, respectively. The effective degradability of CP for the protein sources were 73.1, 63.2, 60.2, 45.9, 72.0 and 64.4, and for the total diet: 70.9, 71.4, 67.7, 65.0, 72.0 and 72.8, respectively. The effective degradability of DM and effective degradability of CP estimated for MBM were lower (P<.05) than all other CP sources. Effective degradability of CP for CM in CM19 was greater (P<.05) than when tested with CM16.5. The effective degradability of DM obtained for the total diet formulated with MBM were lower (P<.05) than all other total diets. The total diet effective degradability of CP for SBM16.5 and MBM were lower (P<.05) than all other total diets tested. The data are interpreted to indicate that MBM is slowly degraded in the rumen, and that CP degradation tended to increase with increasing level of CP in the diet.