Factors Influencing Rumen Fermentation: Effect of Hydrogen on Formation of Propionate

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Abstract
The effect of H on fermentation of lactate, pyruvate, fumarate and succinate by resting rumen microorganisms was investigated. Under N atmosphere, lactate was fermented to yield acetate as the major product (85-100 mol%) and propionate (0-17 mol%) and butyrate (0-3%) as secondary products. Under H there was increased formation of both propionate and total volatile fatty acids. The amount of propionate increased 4-8 times and total volatile fatty acids 2.5-3.2 times. Propionate formation was proportional to the H concentration and reached a maximum at a partial pressure of H of .2 N/m2. With [2-carbon-14] lactate, propionate was formed via the dicarboxylic acid pathway under both N or H. H did not affect significantly the fermentation of pyruvate or succinate. With fumarate under H, propionate and total volatile fatty acids increased 6.8 and 2 times while acetate was unchanged. The mechanism by which H exerts these effects is discussed in relation to the role of methanogenesis in the rumen.