Lactic acid-utilizing bacteria in ruminal fluid of a steer adapted from hay feeding to a high-grain ration.

A mature, rumen-cannulated steer fed Coastal Bermuda grass hay for 8 weeks was adapted to a high-grain ration by stepwise increases in grain over a period of 4 weeks. The grain rations had concentrate-to-roughage ratios of 40:60, 70:30, and 85:15 and were fed for 10, 7, and 11 days, respectively. Numerical estimates of lactate-utilizing bacteria in ruminal fluid of the steer the last 3 days each ration was fed were made by colony counts. Lactate-utilizing bacteria were identified as Megasphaera elsdenii, Peptococcus asaccharolyticus, and Selenomonas ruminantium. Maximal numbers of lactate-utilizing bacteria were observed in the ruminal fluid of the steer during feeding the concentrate-to-roughage ration of 70:30.