Changes Caused by Ethanol in Fermentation Pattern and Membrane Fatty Acid Composition of Rumen Microorganisms

Abstract

In order to utilize ethanol as a feed additive, it is important to know the effect of ethanol on rumen microorganisms: (1) Effect on VFA and gas production was examined in vitro. Mixed rumen microorganisms harvested from a steer fed a diet containing ethanol (5% of feed intake, "EtOH-fed") or a control diet ("EtOH-unfed") were incubated with graded levels of ethanol. Ethanol increased VFA and gas production below 2-3% and decreased above the concentration, and the critical concentration was not different between "EtOH-fed" and "EtOH-unfed "periods. In both periods, percentages of acetate increased and propionate decreased as ethanol increased from 0 to 6%. In "EtOH-fed" period, proportions of valerate and caproate remarkably increased. VFA production by protozoa was not increased by ethanol, and considerably decreased above 3% ethanol.
(2) Effect on membrane fatty acid composition was investigated in vitro. Ethanol (3%) markedly increased proportions of unsaturated fatty acids (UFA) of mixed rumen microorganisms. Experiments with single strains of rumen bacteria showed, that bacteria were grouped into 3 categories, based on the changes in fatty acids caused by ethanol; in Group 1, ratios of UFA to saturated fatty acids (SFA) were enhanced by ethanol, in Group 2, proportions of branched chain fatty acids increased, in Group 3, significant changes were not observed. The greater was inhibition of growth by ethanol, the less significant changes in fatty acid composition were seen. Some rumen bacteria appear to change their membrane fatty acid composition as a way of adaptation to ethanol. In conclusion, ethanol is not only utilized by rumen microorganisms as an energy source, but also exerts considerable influence on lipid metabolism in the rumen. The latter results suggest that ethanol may affect fatty acids supplied to ruminants.