The Effect of Thyroprotein Feeding on the Blood Level of Inorganic Iodine, Protein-Bound Iodine and Cholesterol in Dairy Cows

Abstract

Changes in blood serum protein-bound I2 (PBI) found under normal conditions to reflect the amt. of thyroid hormone in the blood, and plasma cholesterol, shown to have an inverse relationship to thyroid activity, were measured during and after feeding of different dosages of thyroprotein (Protamone) to dairy cows. Inorganic I2 and blood sugar detns also were made. During thyroprotein feeding both inorganic I2 and PBI values increased tremendously above the normal range. After thyroprotein feeding was ended, inorganic I2 decreased rapidly to normal whereas PBI persisted for several mos. at a level higher than prefeeding values. Plasma cholesterol decreased for a time during thyroprotein feeding and then gradually returned to normal. After thyroprotein feeding was terminated, cholesterol rose above the normal level and then gradually returned to normal. Although plasma cholesterol appeared to reflect more accurately the thyroid status of the cows than did PBI, particularly after thyroprotein feeding was ended, neither of these blood constituents could be accurately correlated with dosage of thyroprotein. The possible reasons for these changes are discussed. No changes in blood sugar due to thyroprotein feeding were observed. The injn. of thyrotropic hormone into a steer resulted in an increase in PBI without any increase in inorganic I2. This is further indication that PBI does reflect thyroid status when thyroid activity is increased without the interference of noncalorigenic PBI.