Use of a semicontinuous culture system (RUSITEC) to study the metabolism of ethanol in the rumen and its effects on ruminal digestion

The metabolism of ethanol by rumen micro-organisms and its effects on rumen fermentations have been studied in vitro in a semicontinuous fermentor (RUSITEC). Ethanol introduced in the fermentor at 1, 4 or 8 g d −1 L −1 of rumen juice induced important qualitative and quantitative modifications in the fermentation outputs. Total VFA production was increased from 5 to 40% according to the diet and ethanol concentration. Relative proportions of VFA were modified: caproate concentration increased three times, propionate and isovalerate concentrations decreased significantly in most cases. Methane production was increased. Whatever the ethanol concentration and the type of diet, in vitro digestibility parameters and end-products from solid feedstuffs stayed practically unchanged by ethanol addition. Except with the lowest supply (1 g d −1 L −1 ), ethanol induced an uncoupling effect on the metabolism of rumen bacteria and decreased biomass production. Radioactivity of 2- 14 C ethanol was recovered mainly in acetate (77–80%). Microbial transformation of ethanol in RUSITEC was limited regardless of ethanol concentration. Ethanol had a negligible effect on the digestibility of solid feedstuffs but induced consistent qualitative changes in rumen fermentations. Key word: Ethanol, metabolism, rumen, semicontinuous culture