Effect of Different Ratios of Concentrate and Roughage on Lipid Synthesis by Rumen Microorganisms In Vitro

The effect of different feeding ratios of concentrate to roughage on ruminal lipid synthesis in vitro was examined. Three sheep fitted with a rumen fistula were fed three different ratios (8:2, 4:6 and 0:10) of concentrate and roughage, and their rumen liquor were used for incubation. C-labeled glucose or sodium acetate as substrate was added to cultures of rumen liquor, and they were incubated for 6 h. The total lipid in the culture of the rumen liquor was extracted, and the percentage of C excess was analyzed. The percentage of C excess recovered when incubated with glucose increased with increased ratio of concentrate in the diet. The values of cultures incubated with glucose were higher than those incubated with sodium acetate except the roughage-only feeding. In the roughage-only diet, the percentage of C excess when incubated with sodium acetate was highest of all diets. The recovery percentage of C from glucose increased with increased ratio of concentrate. The recovery percentage of C from sodium acetate addition in only roughage feeding was highest among the three diets. The recovery percentage of C from glucose was markedly higher than that of sodium acetate addition in all feedings. The results indicate that high concentrate feeding facilitates lipid synthesis by rumen microorganisms, and that glucose may be the precursor for lipid synthesis rather than acetic acid. (Asian-Aust. J. Anim. Sci. 2003. Vol