Paper-Lecture16 - Factors I n f l u e n c i n g R u m e n F...

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Factors Influencing Rumen Fermentation: Effect of Hydrogen on Formation of Propionate M. D. SCHULMAN and D. VALENTINO Merck Institute for Therapeutic Research Rahway, NJ 07065 ABST RACT The effect of hydrogen on fermenta- tion of lactate, pyruvate, fumarate, and succinate by resting rumen microorga- nisms has been investigated. Under an atmosphere of nitrogen, lactate was fer- mented to yield acetate as the major product (85 to 100 mole %) and propio- nate (0 to 17 mole %) and butyrate (0 to 3%) as secondary products. Under hydro- gen, there was increased formation of both propionate and total volatile fatty acids. The amount of propionate in- creased 4 to 8 times and total volatile fatty acids 2.5 to 3.2 times. Propionate formation was proportional to the hydro- gen concentration and reached a maxi- mum at a partial pressure of hydrogen of .2 N/m 2. With [2-carbon-14] lactate, pro- pionate was formed via the dicarboxylic acid pathway under both nitrogen or hydrogen. Hydrogen did not affect signif- icantly the fermentation of pyruvate or succinate. With fumarate under hydrogen, propionate and total volatile fatty acids increased 6.8 and 2 times while acetate was unchanged. The mechanism by which hydrogen exerts these effects is discussed in relation to the role of methanogenesis in the rumen. INTRODUCTION In ruminants ingested feed is fermented extensively by a diverse population of anaero- bic microorganisms in the reticulorumen before passing into the lower digestive tract. Major products of this fermentation are volatile fatty acids, acetate, propionate, and butyrate from carbohydrates and amino acids; NH 3 branched chain fatty acids from proteins; gases Received November 7, 1975. CO2 and CH4 ; and increased microbial popula- tion (10). Methanogenic bacteria, Metbanobacterium ruminantium (23)and Metbanobacterium too- bills (19) catalyze the reduction of CO2 with molecular hydrogen to form CH4. The ter- minal electron acceptor for the fermentation is CO2, and its rapid reduction to CH4 is responsible for the low steady state concentra- tion of H2 (.0003 N/m 2) (11). The low concentration of H2 in the rumen permits complete fermentation of substances to pro- duce the maximum yield of adenosine triphos- phate (ATP) and optimal microbial growth. Methanogenesis in the rumen, however, rep- resents a significant loss in dietary energy to the ruminant. As a result, considerable attention has been given to the hypothesis that specific inhibition of methanogenesis would increase feed efficiency (kg feed/kg gain) of ruminants by diverting electron flow from CO2 to an acceptor with nutritional value. Inhibition of rumen methanogenesis causes accumulation of H 2 but in quantities insufficient to account for the quantity of CH4 usually formed (2, 5, 17). This indicates that H2 is used in other reac- tions. Iannatti et al. (13) demonstrated effec- tive intercellular transfer of H2 between rumen species in continuous culture by showing that H2 formed by Ruminococcus albus fermenting glucose is used by Vibrio succinogenes for reduction of fumarate to succinate.
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  • Spring '08
  • Carboxylic acid, Butyrate Acetate Propionate Butyrate Acetate Propionate Butyrate Acetate Propionate Butyrate Acetate Propionate Butyrate Acetate Propionate Butyrate, Acetate Propionate Butyrate

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Paper-Lecture16 - Factors I n f l u e n c i n g R u m e n F...

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