Calculation of utilizable crude protein at the duodenum of cattle by two different approaches

The duodenal how of utilizable crude protein (crude protein minus endogenou s protein) in cows was estimated using dietary parameters, first by multipl e regression and secondly by the addition of microbial protein and undegrad ed feed protein. These estimates were compared with 327 results from experi ments conducted with fistulated cows in Braunschweig-Volkenrode and Rostock -Dummerstorf. The regressions and the measurements for microbial protein sy nthesis as well as feed protein degradation and organic matter fermentation in the rumen were based on the same experimental data set. The prediction of utilizable crude protein (uCP) at the duodenum by regression with digest ed organic matter (kg DOM) and undegraded feed protein (g UDP) as predictin g variables, was more accurate than the value given by microbial protein sy nthesis and rumen protein degradability. The regression model [g uCP = [188 .5 similar to (116.5 (UDP/CP))] DOM + 1.03 UDP] had the highest coefficient of determination (r(2) = 0.91) and the lowest coefficient of variation (cv = 8.6); indicating the model's superiority over the other method of estima tion.