Alteration of Activity of Thyroid Gland of Beef Cattle with Testosterone.

Summary and Conclusions 1. Testosterone injected intramuscularly at the rate 1 mg/kg of body wt per week in beef heifers and steers from 500 to 800 lb live wt had the following effects: a) Increased average daily gain and decreased feed requirements per unit gain, b) Increased weight of the thyroid glands, c) Increased secretory activity of the thyroid gland, d) Decreased stores of thyroxine in the thyroid gland. 2. Correlations between thyroid gland activity and growth rate are suggested as indicating a possible mode of the action of testosterone in affecting growth of beef cattle. 3. A method is described using the time of asphyxiation of thiouracil-treated mice as a measure of thyroxine content of the thyroid gland.