Effects of Solids and Liquid Flows on Fermentation in Continuous Cultures. IV. pH and Dilution Rate

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Abstract
The purpose of this study was to examine the effects of various liquid dilution (D) rates and pH levels, at a constant solids retention time, on metabolism and fermentation patterns of rumen microbes in continuous culture. The D rates were 4, 8, 12 and 16%/h. At each D rate, fermentations were conducted at pH 4.5, 5.5, 6.5 and 7.5. Under these conditions, pH 6.5 was found to be optimum for fiber and organic matter digestion, with only small D effects. Total nonstructural carbohydrate digestion was high (89 to 95%) at all pH and D rate combinations. As pH increased from 5.5 to 7.5, the molar percentage of acetic acid increased while that of propionate and butyrate decreased. These ratio changes were due to a large increase in acetate production (mol/24 h) accompanied by a small increase in propionate and a decrease in butyrate production. The D rate increases caused propionate molar percentage and production rate to increase, but had little effect on butyrate and acetate. Protein digestion and microbial growth and efficiency were affected by specific sets of pH and D conditions. At pH 4.5 and 7.5, at the 4%/h D rate, values for these characteristics were high, but were decreased by increases in D. The data also suggest that energetic uncoupling resulted from high D rates at these pH levels. At pH 6.5 protein digestion, microbial growth and efficiency were high at all D rates, with increases as D rate increased. Ar pH 5.5, protein digestion and microbial growth were low at all D rates. Osmotic pressure changes were found to have little effect on fermentation or metabolism. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.

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