Abstract
Summary
Chlortetracycline was fed to chicks at levels of 10, 50, 500, and 1000 mg/ kilo of diet. The data show that this treatment significantly increased the size of the thyroid gland. Examination of the data by regression analysis gave b-values to show that antibiotic dosage up to 100 mg/kilo of diet was correlated to increase in thyroid size. Increasing the antibiotic dosage above this level did not increase the thyroid size at the same rate. Since the growth of the chicks was not depressed and the thyroid was not enlarged as much as it was when thiouracil was fed, it appears that chlortetracycline did not duplicate the action of thiouracil.
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