A note on the flora and fauna in the rumen of steers fed a feedlot bloat-provoking ration and the effect of penicillin.

A study was made of the predominant culturable bacteria and ciliate protozoa present in the rumen of two steers that were regularly bloating on a pelleted ratio containing 22% alfalfa meal, 16% soybean oil meal, 61% barley, and 1% common salt. The ruminal microorganisms in the two animals differed as indicated by a high total culture count of bacteria, an almost complete absence of ciliate protozoa, a low pH, and a difference in the proportions of presumptively identified predominant bacterial groups in one animal (steer 26) as compared with the other (steer 32). The first exposure of the animals to procaine penicillin (75 or 150 mg per day on 2 successive days) resulted in an abnormal ruminal flora 31 hr after the first treatment as indicated by drastic drops in total and cellulolytic bacterial counts and a change in the proportions of predominant bacterial groups. The animals refused feed for 32 to 48 hr after the first treatment. After feed consumption resumed, further treatment with 75 mg penicillin on 4 successive days did not appear to greatly alter the flora and did not result in feed refusal in animal 32. In animal 26, amounts of penicillin progressing from 50 to 200 mg per day did not result in feed refusals and observations on rumen ingesta samples during this period indicated a decrease in total bacterial count, a great increase in numbers of ciliate protozoa, a higher pH, and a change in the proportions of predominant bacterial groups so that the ruminal picture was much more similar to that of animal 32 than to its own during the pre-penicillin period. Bloat was not relieved except during the period of feed refusal. The results indicate that the ruminal flora rapidly adapts to penicillin and that bloat of the feedlot type can occur in animals with widely differing numbers and kinds of bacteria and protozoa. Feedlot bloat does not appear to be correlated with the occurrence or numbers of any of the individual predominant groups of bacteria cultured.