In situ evaluation of the protein value of wheat grain corrected for ruminal microbial contamination

BACKGROUND: Uncorrected and microbial corrected in situ estimates of ruminal effective degradability (RED) of dry matter (DM), organic matter (OM) and crude protein (CP) and intestinal effective digestibility (IED) of DM and CP of a wheat grain sample were obtained by a simplified method using a sample pooled from rumen-incubated residues representing rumen outflow of undegraded food. Uncorrected values of RED of DM and CP were also obtained by the usual mathematical integration method. The study was performed in three rumen and duodenum cannulated wethers. RESULTS: Uncorrected values of RED of CP were similar either for the mathematical integration or this simplified method (82.4% vs. 82.2%). Microbial contamination in the rumen led to small underestimations (P < 0.05) of RED of DM (87.9% vs. 88.1%) and CP (82.2% vs. 82.8%) and to small overestimations (P < 0.05) of IED for DM (66.5% vs. 66.1%) and CP (87.7% vs. 87.3%). Accumulative errors resulted in overestimations (P < 0.05) of the intestinal digested fractions of DM (1.8%) and CP (4.0%). CONCLUSION: Corrected values of intestinal digested CP show that the protein value of wheat is closely related to the microbial protein synthesis derived from its OM rumen fermentation. This synthesis and the content of intestinal digested undegraded protein may be respectively higher and lower than is usually assumed in feed tables. Copyright © 2009 Society of Chemical Industry