Comparison of the Metabolism of Sodium Iodide and 3,5-Diiodosalicylic Acid in Dairy Cattle

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Abstract
Three cows were dosed orally twice daily with diiodosalicylic acid (DI131S) and NaI125 plus Ce144 as a non-absorbed marker. Ruminal absorption and abomasal secretion of iodine from NaI were greater (P< .01) than from DIS. Below the duodenum, absorption of DIS paralleled that of iodide. Because of reduced abomasal secretion of DIS, fecal excretion of iodide was four times that of DIS. Secretion into milk and thyroid accumulation of iodide were over four times that of DIS. Four additional cows received single doses of NaI131 in one period followed by DI131s in a later period. Average 7-day I131 excretions from NaI compared to DIS doses were 13.5 and 3.3% (P .01) in milk, 31.5 and and 81.0% (P<.01)inurineand39.0and7.7% (P< .01)infeces. Although high plasma protein binding of DIS reduced availability of iodine from this source to the thyroid and mammary gland, DIS was rapidly cleared in the urine, probably as the glycine conjugate. The stability of DIS in trace-mineralized salt must be weighed against its relative unavailability compared to iodide.