Effect of thyroid status and thiocyanate on absorption and excretion of iodine by cattle.

Effects of throidectomy or iodine-131, thyroprotein feeding, and thiocyanate dosing on radioiodine metabolism in the bovine were studied in 34 animals. Two thyroidectomized calves excreted 44% more radioiodine in urine and 38% less in feces than two thyroid-tact calves. Oral thiocyanate increased urinary radioiodine 32% in throidectomized and 46% in intact calves while reducing fecal radioiodine 48% in throidectomize and 11% in intact calves. Urninary radioiodine clearance of two heifers was increased 52% by thiocyanate, but urine flow was not affected. Percentages of radioiodine doses cycled through the abomasum daily and recovered from digestive tracts at slaughter, respectively, were: 12 thyroid-intact cows, 468 and 77; two intact cows fed 10 g sodium thiocyanate daily,64 and 41; 10 thyroid-damagedcows, 506 and 149; and four thyroid-damaged cows fed 8 g thyroprotein daily, 372 and 93. Thyroid damage had little effect on gastric radioiodine secretion but increased total digestive tract radioiodine because of greater volume of tract contents. Inhibition of gastric radioiodine secretion by thiocyanate reduced the digestive tract radioiodine pool. The digestive tract iodine pool may conserve iodine by reducing loss in urine.