The effects of protozoa and of supplementation with nitrogen and sulfur on digestion and microbial metabolism in the rumen of sheep
1994
Hegarty, R.S. | Nolan, J.V. | Leng, R.A. (New England Univ., Armidale (Australia). Dept. of Biochemistry)
In one experiment, 12 faunated and 12 fauna-free sheep were offered a basal diet of chopped wheaten straw with or without S and urea-nitrogen N supplements. S supplementation increased the rate of straw digestion and the concentration of volatile fatty acids (VFA) in the rumen while reducing methane production. The presence of protozoa did not significantly affect this response, although it increased rumen H2S concentration. In contrast, the response of rumen fermentation to a urea supplement was affected by the presence of protozoa. Ammonia and total VFA concentrations in the rumen were not affected by protozoa, but the molar proportions of butyrate and isoacids in rumen VFA were greater in faunated sheep. In a second experiment, the chemical composition of rumen bacteria of faunated and fauna free sheep was further investigated. In both groups, bacteria associated with the particle-phase of digesta contained a higher proportion of lipid and a lower proportion of N than did fluid-phase bacteria. Fluid-phase bacteria from faunated sheep tended to have more lipid and less N in their DM than did those from fauna-free sheep. It was concluded that the presence of protozoa enables sustained fermentation of diets low in rumen available N and also increases the lipid content of rumen fluid-phase bacteria.
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