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Four Holstein steers fed with Sorghum silage were used to examine the effect of fumaric acid supplementation (20g/kg. diet dry matter (DM)) on methane production, rumen fermentation, blood metabolism and feed digestibility. The protozoal population in the rumen was unaffected by fumaric acid supplementation. The postprandial ruminal concentration of ammonia-N decreased, and that of total volatile fatty acids tended to be higher with fumaric acid supplementation. The proportion of ruminal acetic acid was unaffected, but that of propionic acid increased and that of butyric acid decreased by fumaric acid. The postprandial blood plasma concentration of glucose was increased, whereas that of urea-N was decreased by fumaric acid. The plasma concentration of most of free amino acids was unaffected. Daily methane production decreased by 23.0% and carbon dioxide production decreased by 20.5% with fumaric acid supplementation. Apparent digestibility of dry matter and of neutral detergent fiber were not influenced by fumaric acid. These results indicated that fumaric acid was converted to propionic acid by rumen microorganisms, and that methane production from the rumen was reduced without lowering the ability to digest dietary fiber. However, some dietary conditions that alter the effectiveness of fumaric acid and the long term effect remain to be examined.
ERUDEN et al. (Mon,) studied this question.