Effects of Nitrate Combined with Fumarate on Methanogenesis, Fermentation, and Cellulose Digestion by Mixed Ruminal Microbes in vitro

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Mixed ruminal microbes from the rumen of a goat were incubated with nitrate or nitrite in a growth medium containing starch and cellulose. The rate of nitrate reduction was 2.5-fold faster than the rate of nitrite reduction, which brought about the accumulation of nitrite. The increase in nitrate increased the peak nitrite concentration, and prolonged the time for nitrite to disappear. The addition of nitrate decreased methanogenesis partly by the consumption of electrons, but to a greater extent by the suppression of fermentation due to accumulated nitrite. The addition of fumarate increased the rate of nitrate reduction, and to a greater extent increased the rate of nitrite reduction, which alleviated the adverse effect of nitrite on fermentation and cellulose digestion. Consequently, the combination of fumarate and nitrate decreased methanogenesis without the suppression of fermentation or a decrease in propionate production.