Improvement of the Streptomyces griseus method for degradable protein in ruminant feeds

The methods of Krishnamoorthy et al. [Krishnamoorthy, U., Sniffen, C.J., Stern, M.D., Van Soest, P.J., 1983. Evaluation of a mathematical model of rumen digestion and an in vitro simulation of rumen proteolysis to estimate the rumen undegraded nitrogen content of feedstuffs. Br. J. Nutr. 50, 555–568] and Roe et al. [Roe, M.B., Sniffen, C.J., Chase, L.E., 1990. Proc. Cornell Nutrition Conference, Dept. of Animal Science, Cornell University, Ithaca, NY, pp. 81–88], and a new one presented in this paper have been compared, and a revised procedure is proposed using a fixed ratio of enzyme to true protein (TP) determined by tungstic acid precipitation. A comparison of the three methods shows that they are statistically different. The ratio of enzyme has also significant effect (p>0.01) on the estimate of degradable nitrogen when compared to the fixed concentration of enzyme in the original method. The effect of buffer pH (6.7 vs. 8) on degradation of protein sources was also statistically significant (p>0.05) with somewhat higher degradation at pH 8.