Effects of isoacids, urea, and sulfur on ruminal fermentation in sheep fed high fiber diets

The effects of isoacids, urea N, and S on ruminal fermentation of sugarcane bagasse- or corn stover-based diets were studied in sheep. Acetate production was taken as a measure of the fermentation rate. For the sugarcane bagasse diet, neither urea nor S supplementation changed ruminal acetate production. When N and S were combined, acetate production was 44% higher (3.16 vs. 2.18 mol/d). Similar effects were noted for the corn stover diet. Increasing the level of isoacids from .1 to .2 g/kg BW per d in the diet did not change acetate production for either diet. However, N supplementation of the sugarcane bagasse diet containing the low level of isoacids resulted in a 49% greater acetate production (2.86 vs. 1.91 mol/d). Acetate production was 90% higher (3.74 vs. 1.97 mol/d) when the diet containing the high level of isoacids was supplemented with N. The corresponding increases for corn stover were 12% (2.64 to 2.95 mol/d) and 35% (2.88 to 3.87 mol/d). The results suggest that NH3 N provided by the basal diet was more limiting than isoacids. Once the N deficiency was corrected, isoacids became limiting. Ruminal digestion of high fiber diets low in N was improved by supplementation with urea, isoacids, and S.