Utilization of Ethanol and Its Effect on Fatty Acid Patterns in Ruminants

In an in vivo experiment designed as a Latin-square, an ethanol solution was continuously infused for 5 weeks into the tureen of 4 lactating Holstein cows fed 2 rations (a milk fat depressing, high-grain and a 40% hay control). Ethanol (1300 to 1500 ml/day) infusion caused a three-to fourfold increase in the proportion of iso-valeric acid in the rumen fluid, which was accompanied by an approximately equimolar decrease in propionic acid. Also the concentrations of n-valeric and caproic acids were higher in the rumen during the ethanol infusion period. Ethanol disappeared more rapidly from the rumen ingesta of cows fed the high grain diet. Milk fat was increased by ethanol infusion with both rations. An adaptation to alcohol by rumen microorganisms was demonstrated in vitro. The importance of ethanol in the synthesis of iso-valeric acid, as studied in vivo, was also demonstrated in vitro by a higher specific activity of the C5 fraction (iso-valeric and n-valeric acid). An increase in ruminal iso-valeric acid with a concomitant decrease in the propionic acid concentration during in vivo ethanol infusion, coupled with a greater in vitro incorporation of ethanol-2-C-14 presumably into the iso-valeric acid, may suggest a possible common intermediate for the bio-synthesis of these acids in the rumen.