Effects of dietary protein and carbohydrate source on rumen fermentation and nutrient flow in sheep

The effects of decreasing levels of rumen degradable protein (RDP) and nons tructural carbohydrate (NSC) (Diet 1: 74% RDP and 38% NSC; Diet 2: 57% RDP and 32% NSC; Diet 3: 48% RDP and 23% NSC) were studied in cannulated sheep. Total volatile fatty acid (VFA) content rose in response to increasing NSC content. The molar ratio of acetate to propionate was the narrowest for Di et 1. Ruminal concentrations of ammonia and urea increased in response to t he rising level of RDP. Flow of organic matter (OM) to the duodenum was inc reased for Diet 3, which resulted in the lowest apparent and true ruminal d igestion of OM. Duodenal flow of total nitrogen (N) increased as RDP conten t decreased. The highest quantity of undegraded feed protein in duodenal di gesta was measured in sheep fed Diet 3. Microbial N flow and microbial effi ciency were unaffected by the diets. These results indicate that an NSC lev el lower than 25% and an RDP content lower than 50% did not exert any negat ive effect on microbial N production. This phenomenon supports the theory t hat if the level of RDP is lowered with a concomitant decrease in NSC, unco upled fermentation cannot be observed.