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Antibiotics in Rumen Digestion and Synthesis III. The Effect of Aureomycin on Rumen Microorganisms, with Special Reference to the Streptococci and Coliform Groups^{1, 2,}

Departments of Dairy, Bacteriology, and Agricultural Chemistry, Michigan Agricultural Experiment Station, East Lansing

ABSTRACT

The use of some antibiotics and feed supplements containing antibiotics to stimulate growth in certain farm mammals has been established, but the mode of action of these selective or inhibitory chemical agents is relatively unknown insofar as their effect on the microorganisms in the bovine rumen is concerned.

Bartley et al. (2) could not find a consistent difference between rumen microorganisms in control and aureomycin-fed calves by using a direct microscopic method. Neumann et al. (22) observed that the total bacterial counts in the rumen ingesta of aureomycin-fed heifers were about the same as in control heifers, although the types of microorganisms were less diverse when aureomycin was fed. This observation suggested that aureomycin can inhibit some of the naturally-occurring rumen flora. In an in vitro study of cellulose digestion with tureen microorganisms, Wasserman et al. (31) found that low concentrations of penicillin and streptomycin stimulated the cellulolytic microorganisms and neomycin was stimulatory in all concentrations used, whereas chloromycetin inhibited the eellulolytic microorganisms.

¹ Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal article No. 1443.

² This study was made in part with funds provided by the Research and Marketing Act of 1946, through a cooperative project between the Michigan Agricultural Experiment Station and the Bureau of Dairy Industry.

³ This article is part of a dissertation presented to the Faculty of the Graduate School of Michigan State College in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

⁴ Present address: Department of Animal Husbandry, Cornell University, Ithaca, N. Y.