Role of Megasphaera elsdenii in the Fermentation of dl -[2- 13 C]lactate in the Rumen of Dairy Cattle

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Abstract
Since Megasphaera elsdenii ferments a variable part of dl-lactate to butyrate, measurement of the percentage of dl-lactate fermented to propionate via the acrylate pathway in rumen contents will underestimate the participation of M. elsdenii in the dl-lactate fermentation. The percentage of dl-[2-13C]lactate fermented via the acrylate pathway and the percentage of dl-lactate fermented to butyrate can be measured with 13C-FT (Fourier transform)-nuclear magnetic resonance. On the average, the contribution of M. elsdenii to dl-lactate fermentation in the rumen of dairy cattle was found to be 74% (standard deviation, 13%), but differed with animal or diet. After feeding a cow readily fermentable carbohydrates, the contribution of M. elsdenii to the fermentation of dl-lactate increased as a consequence of catabolite repression in other dl-lactate-fermenting bacteria.