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I¹³¹ Uptake in Calves Fed Chlortetracycline

Ohio Agricultural Experiment Station, Wooster

ABSTRACT

The growth-stimulating effects of chlortetracycline and other antibiotics in dairy calves have been reviewed recently by Lassiter (2), who discussed various theories of their mode of action. Calesnick et al. (1) reported that both chlortetracycline and penicillin, fed at the rate of 1 mg/kg of feed to two groups of four rats, had a goitrogenic effect as measured by increased thyroid weight and decreased I¹³¹ uptake. The purpose of this experiment was to determine whether or not growth stimulation in calves resulting from chlortetracycline might be associated with thyroid function.

In this study, I¹³¹ uptake was measured in calves which had been fed chlortetracycline to 12 weeks of age.

In Experiment I (1953), 16 Jersey calves were used, nine of which were fed 20 mg. of chlortetracycline (Aurofac-2A) per lb. of dry feed. The dry ration consisted of high-roughage pellets (two parts ground alfalfa hay and one part a simple grain mixture).