Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/1996
Publication Date: N/A
Interpretive Summary: When ruminant animals are fed large amounts of cereal grain, the rate of ruminal fermentation can be so fast that ruminal pH decreases. Ruminal acidosis depresses food intake and in extreme cases even causes death of the animal. Ruminal acidosis is caused by the overgrowth of Streptococcus bovis, a bacterium that produces large amounts of lactic acid. Animals that were gradually adapted to cereal had lower numbers of S. bovis than expected. S. bovis was inhibited by a compound that was produced by lactobacilli. Compounds like the one from ruminal lactobacilli may provide a mechanism of modifying ruminal fermentation, preventing acidosis and other ruminal disorders, and improving the health and well being of ruminant livestock.
Technical Abstract: Cattle that were fed an all forage diet had higher numbers of S. bovis than lactobacilli (3 x 10 7) versus 4 x 10 3). Gradual adaptation of the cattle to 80% cereal grain caused only a modest decline in ruminal pH (always >/- 5.6), but there was a dramatic decrease in S. bovis and an increase in lactobacilli. The lactobacilli were more resistance to low pH than the S. bovis isolates, but pH alone could not explain the antagonism between ruminal S. bovis and lactobacilli. The ruminal lactobacilli were identified as Lactobacillus fermentum, a bacterium that produces a bacteriocin. Agar overlays and zones of S. bovis clearing supported the hypothesis that L. fermentum was producing a bacteriocin that inhibited the growth of S. bovis in the rumen.