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Predominant Bacteria in the Rumen of Cattle on Bloat-Provoking Ladino Clover Pasture¹

Dairy Cattle Research Branch, USDA, Beltsville, Maryland and Department of Animal Husbandry, Mississippi State College, State College

ABSTRACT

A study was made on the microorganisms in the rumen of six yearling steers pastured on bloat-provoking Ladino clover. Three animals were selected for study on the basis of being good bloaters and three were nonbloaters. Studies on the bloaters were made before and 24 hr. after they were treated orally with 50 mg. of procaine penicillin to prevent bloat. There were no significant differences between animal groups in pH of ruminal contents, counts of cellulolytic bacteria, total anaerobic bacterial counts, or the occurrence of 11 presumptively identified bacterial groups. Counts of facultatively anaerobic streptococci were significantly depressed in the penicillin-treated group, but no other effects of treatment appeared to be significant. The means of the total anaerobic bacterial counts of the bloaters were higher than those of the two other groups, but the difference only approached significance. It is evident that the occurrence of bloat in animals consuming Ladino clover is not related to large differences in the numbers or species of ruminal microorganisms.

The bacterial flora of the rumen of these Ladino clover-pastured steers, culturable in rumen fluid agar medium, differed somewhat from usual, in that the total anaerobic counts were high (5.8-8.0 billion per gram), the proportions of cellulolytic bacteria (ruminococci and Bacteroides succinogenes) were very low, a species of anaerobic homofermentative lactobacilli was among the predominant bacteria, and the proportions of the genus Butyrivibrio were high and those of the genus Lachnospira were unusually high.

¹ This research was conducted under Research and Marketing Act contract No. 12-14-100-900(52) between the Mississippi State College Agricultural Experiment Station and the U. S. Department of Agriculture.

² Present address, Department of Agricultural Chemistry, Mississippi State College, State College, Mississippi.