RUMEN AVAILABILITIES OF NONSTRUCTURAL CARBOHYDRATE AND PROTEIN ESTIMATED FROM IN-SITU INCUBATION OF INGREDIENTS VERSUS DIETS

Four diets formulated for high and low levels of rumen available nonst ructural carbohydrate and protein were incubated in situ. Ingredients used to formulate these diets were incubated separately to determine i f the degradation characteristics of the mixed diets could be predicte d from the ingredients. A second objective was to determine if the lev el of rumen available nonstructural carbohydrate or protein affected d egradation. Rumen availability of nonstructural carbohydrate was predi cted within 4% and rumen available protein within 6% when estimates we re made from ingredients versus the total diets. Diets that contained lower levels of rumen available protein had slower rates of degradatio n of dry matter, protein, and nonstructural carbohydrate than predicte d from ingredients but rate estimate differences were not large enough to cause significant differences in actual versus predicted ruminal a vailabilities. Lower ruminal ammonia and(or) peptides may have inhibit ed degradation rate when cows were fed lower rumen available protein d iets. Diets can be formulated for different ruminal availabilities of nonstructural carbohydrate and protein when these estimates are made f rom ingredients incubated in situ. Degradation rates of diets may be o ver-predicted if slowly degrading protein sources are used.