Effect of monensin on total volatile fatty acid production by steers fed a high grain diet.

Four rumen-fistulated steers, averaging 315 kg during two experimental periods were used in a replicated 2 X 2 Latin square study designed to determine the effects of monensin supplementation on rumen volatile fatty acid (VFA) production, pH and liquid volume. A 72% steam-flaked, sorghum grain diet was fed twice daily at 0700 and 1700 h at 2.0% of live body weight. Production rates were determined at 11 times during a 24-h feeding cycle by short-term in vitro incubations of whole rumen contents. Monensin increased moles/100 mol (P less than .05) and production rate (mumoles X liter-1 X min-1; P greater than .01) of propionate and depressed moles/100 mol (P less than .01) and production rate (P less than .05) of butyrate. Moles of acetate/100 mol were not affected (P greater than .05) by monensin. Daily propionate production (moles) was increased (P less than .01) by 37% by monensin. Monensin increased total production of acetate (11%) and total VFA production (16%), both nonsignificantly. Both rumen pH and liquid volumes were increased nonsignificantly by monensin.