Mixed ruminal microbes of cattle produce isopropanol in the presence of acetone but not 3-D-hydroxybutyrate.

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 9 h. No isopropanol was present in any sample at 0 h, 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 6 h and significantly larger amounts from 6 to 9 h. With starch as the energy substrate, production from 6 to 9 h was 3.8 micromol/min per liter of rumen fluid and 3.7 micromol/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.