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The Effect of Chlortetracycline Feeding on In vitro Cellulose Digestion by Rumen Microorganisms^1,2,

Iowa Agricultural Experiment Station, Ames

Abstract

Six collections (at weekly intervals) of rumen microorganisms were made from each of 14 lactating cows, seven of which had received 240 mg. of chlortetracycline per animal daily from an early age. After the collection of the first three samples from the treated cows, the antibiotic was removed from the diet.

Cellulose digestion was measured in vitro. During the first three collection periods microorganisms from control cows (cows receiving no chlortetracycline) digested 45.3% of a purified cellulose (Solka-Floc) as compared to 34.4% for inocula from cows receiving the antibiotic. When alfalfa hay was used as the substrate, cellulose digestion was 59% for the controls and 45.1% for cows receiving the antibiotic.

During the three subsequent collection periods when chlortetracycline was removed from the diet of the treated cows, digestion was 51.4% for controls and 51.3% for animals formerly fed the antibiotic when Solka-Floc was used as the substrate and 66.0% and 65.2%, respectively, when alfalfa hay was used as the substrate.

¹ Journal Paper No. J-2851, Iowa Agricultural Experiment Station, Ames, Iowa. Project No.1124.

² Supported in part by funds provided by American Cyanamid Co., Pearl River, New York.