Comparison of actual and predicted amino acid contents in the duodenal digesta of dairy cows

In this experiment on three dairy cows with the ruminai and duodenal T-cannulas,the actual and predicted amino acid (AA) profiles of the protein fraction flowed to the small intestine were compared. The prediction was calculated by two methods: with the use of mean published AA profile of microbial protein and of experimentally determined one. The actual AA profile of digesta protein was corrected for glycine (Gly) of bile origin. In comparison to the published AA profile of microbial protein the use of the actual one did not contribute to an improvement of prediction accuracy (mean prediction error: 7.36 vs. 7.54%,respectively). Inaccurate determination of AA composition of undegraded feed protein and the insufficient correction for Gly of bile origin were the probable sources of the residual variability.