Mixed Ruminal Microbes of Cattle Produce Isopropanol in the Presence of Acetone But Not 3-d-Hydroxybutyrate

Abstract

The objective was to evaluate the ability of mixed rumen microbes to synthesize isopropanol from acetone or 3-d-hydroxybutyrate. Rumen fluid from seven mature, nonpregnant, dry Holstein cows was incubated with starch or cellulose and additions of acetone, 3-d-hydroxybutyrate, or saline. Rumen fluid was analyzed for isopropanol after 0, 3, 6, and 9h. No isopropanol was present in any sample at 0h, and none was present in incubations containing saline or 3-d-hydroxybutyrate at any subsequent time. Incubations that included acetone produced small amounts of isopropanol from 0 to 3 and 3 to 6h and significantly larger amounts from 6 to 9h. With starch as the energy substrate, production from 6 to 9h was 3.8μmol/min per liter of rumen fluid and 3.7μmol/min per liter with cellulose as the energy substrate; however, these values did not differ significantly. Mixed rumen microbes could synthesize isopropanol from acetone but not from 3-d-hydroxybutyrate, and rumen microbial metabolism of acetone was the likely source of plasma isopropanol seen in ketotic ruminants.