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Effect of Glucocorticoids on Thyroid Function of Cattle¹

Department of Dairy Husbandry, University of Missouri, Columbia

ABSTRACT

The influence of two glucocorticoids upon the thyroidal-I¹³¹ release rate of cattle is reported. After the normal release rate of each animal was determined during a five-day period (recycling of I¹³¹ blocked by a goitrogen), seven cows were injected with hydrocortisone at the rate of 75 mg/100 lb. body weight per day for six days. Of these cows, five showed varying degrees of depression of thyroidal-I¹³¹ release, whereas two showed an increased release rate. Meticorten, a synthetic glucocorticoid, injected in eight heifers at the rate of 40 mg/100 lb. body weight per day, showed a variable increased release rate in six animals, whereas two showed a slight depression. These data suggest that hydrocortisone at the level administered tends to depress thyrotropin and thyroxine secretion, whereas meticorten tends to stimulate thyroid function. The causes of the individual differences in response in cattle to these glucocorticoids is not known, but may be related to individual secretion rates of other hormones. It is suggested that cattle with low thyroxine secretion rate, which is further depressed by increased secretion of hydrocortisone associated with parturition, would show low PBI and high 17-hydroxy-corticosteroid values characteristic of cows with ketosis.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 2168. Approved by the Director.

² Aided in part by a grant from the U.S. Atomic Energy Commission [Contract No. AT(11-1)-301].