The objective of this work was to evaluate the ruminal disappearance and nitrogen intestinal digestibility of 18 concentrate feedstuffs and four grasses, using an in vitro inhibitor with HCL-pepsin-pancreatin solutions and the three-step method. The disappearance of nitrogen compounds of feedstuffs was determined at 0 and 2 hours using 1.875 mg of N incubated on each three vessels. One of the vessels was submitted to intestinal digestion. On the second method, approximately 5 g of samples were incubated, during 16 hours, in the rumen of a steer fed a diet with 60:40 forage to concentrate ratio. After the incubation period, samples containing 15 mg of residual N were incubated in HCL-pepsin-pancreatin solutions during 25 hours. Data of intestinal digestibility of ruminal undegradable protein was not constant. The inhibitor method was more efficient to evaluate and predict kinetic parameters of ruminal degradation and the three-step method for intestinal digestibility of ruminal undegradable protein.
degradability; intestinal digestibility; ruminal undegradable protein
