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The Mode of Action of Antibiotics in the Nutrition of the Dairy Calf. I. Effect of Terramycin Administered Orally on the Performance and Intestinal Flora of Young Dairy Calves¹

Departments of Dairy and Microbiology and Public Health, Michigan State University, East Lansing

ABSTRACT

An experiment was conducted to investigate the effects of feeding terramycin on the performance and intestinal microflora of dairy calves from 3 days to 9 weeks of age. Terramycin administration increased significantly the rate of weight gain by 33% above that of the control animals. Appetite and feed efficiency were significantly increased. The incidence of scours was low and was not affected by the treatment. Terramycin was detected in the feces 6 to 9 hours after the first feeding. High concentrations of terramycin were found in the feces during continuous feeding of terramycin and the antibiotic was also present in the urine.

Bacteriological studies revealed no marked difference in total and coliform counts attributable to the feeding of terramycin. However, there was a significant decrease in the number of enteric streptococci when terramycin was administered. Antibiotic sensitivity assays indicated an increase in the number of resistant strains of coliforms and enteric streptococci in the feces of calves fed terramycin. The normal metabolism of enteric streptococci appeared to be impaired by the presence of terramycin in vivo and in vitro. These bacteriological studies indicated that improved techniques should be used to determine the extent to which antibiotics affect the intestinal flora of animals.

¹ Published with the approval of the director of the Agricultural Experiment Station as Journal Article No. 1858.

² This article is part of a dissertation presented to the faculty of the College of Agriculture of Michigan State University in partial fulfillment of requirements for a Master's Degree.

³ Present address: c/o DUQUESNE S.A., Montfort (Eure), France.

⁴ Present address: Kansas State College, Manhattan.