COMPARISON OF IN-SITU AND IN-VITRO TECHNIQUES FOR MEASURING RUMINAL DEGRADATION OF ANIMAL BY-PRODUCT PROTEINS

Ruminally undegraded protein (RUP) values of blood meal (n = 2), hydro lyzed feather meal (n = 2), fish meal (n = 2), meat and bone meal, and soybean meal were estimated using an in situ method, an inhibitor in vitro method, and an inhibitor in vitro technique applying Michaelis-M enten saturation kinetics. Degradation rates for in situ and inhibitor in vitro methods were calculated by regression of the natural log of the proportion of crude protein (CP) remaining undegraded versus time. Nonlinear regression analysis of the integrated Michaelis-Menten equa tion was used to determine maximum velocity, the Michaelis constant, a nd degradation rate (the ratio of maximum velocity to the Michaelis co nstant). A ruminal passage rate of 0.06/h was assumed in the calculati on of RUP. The in situ and inhibitor in vitro techniques yielded simil ar estimates of ruminal degradation. Mean RUP estimated for soybean me al, blood meal, hydrolyzed feather meal, fish meal, and meat and bone meal were, respectively, 28.6, 86.0, 77.4, 52.9, and 52.6% of CP by th e in situ method and 26.4, 86.1, 76.0, 59.6, and 49.5% of CP by the in hibitor in vitro technique. The Michaelis-Menten inhibitor in vitro te chnique yielded more rapid CP degradation rates and decreased estimate s of RUP. The inhibitor in vitro method required less time and labor t han did the other two techniques to estimate the RUP values of animal by-product proteins. Results from in vitro incubations with pepsin HCl suggested that low postruminal digestibility of hydrolyzed feather me al may impair its value as a source of RUP.