Influence of Chlortetracycline on in Vitro Cellulose Digestion by Bovine Rumen Microorganisms

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Abstract
Rumen inocula from Aureomycin-fed cows consistently digested, in an artificial rumen, a lower percentage of cellulose (73%) than those from control cows (85%). Aureomycin levels in the rumen liquid of the cows were 0.08 [mu]g/ml 16 hours after, and 0.22 [mu]g/ml 4 hours after, feeding 240 mg of the antibiotic. Addition of 2.4, 1.6, 0.8, and 0.4 [mu]g/ml, respectively, of Aureomycin in a fermentation mixture in the artificial rumen severely inhibited digestion of cellulose by the microorganisms from the control cows. The same additions had comparatively little effect on the digestion of cellulose by inocula from the Aureomycin-fed cows. Plate counts also indicated that rumen microflora are affected by the administration of Aureomycin, but most of the inhibitory effect is lost after a period of adjustment by the microorganisms. Emergence of strains of Pseudomonas and Monilia that have the ability to inactivate Aureomycin was shown.