Protein evaluation of cattle compound feeds: comparison of in sacco measurements and tabular values

The supply of true protein to the small intestine (DVE) and the degraded protein balance (OEB) of 29 experimental compound feeds were estimated in the rumen and intestine of dairy cows (reference), using the nylon bag technique. DVE and OEB were also calculated from tabulated values of the ingredients, taken from the Dutch CVB-tables, assuming additive effects. Reference DVE was on average 11 g/kg DM lower and OEB 6 g/kg DM higher than tabulated values, resulting from a higher rumen degradability of protein (-5.5 percentage units) and lower intestinal digestibility of rumen undegradable protein (-2.0 percentage units) and a lower rumen degradability of starch (+5.8% units) and DOM-content (+27 g/kg DM). The possible causes of these differences are discussed. After elimination of systemic differences, residual errors between reference and tabular values amounted to 5.9 and 14.9% for DVE and OEB, respectively. It is concluded that a reasonable relation exists between DVE- and OEB-content of compound feeds based on tabular values for the ingredients and those calculated from in sacco measurements.