Effects of Feeding Potassium Iodide, 3,5-Diiodosalicylic Acid, or L-Thyroxine on Iodine Metabolism of Lactating Dairy Cows

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Abstract
Three Jersey cows were fed daily 1.3 g I as KI, 1.3 g iodine as 3,5-diiodosalicylic acid (DIS) or no supplemental iodine in 3 periods of a Latin square design. In each period, Nal125 was administered twice daily in capsules for 21 days. Single doses of I131 -labelled L-thyroxine were injected intravenously on the 12th day of NaI125 dosing. Iodine-125 excretion was only slightly affected by DIS but KI caused a 34% reduction in milk I125 and a 38% increase in urine I125. Both compounds reduced excretion of I131 from thyroxine into milk. Urinary I131 excretion was highest from cows fed KI and lowest from those fed DIS. Neither supplement significantly influenced fecal I131 or I125 excretion. In another experiment, 4 cows were dosed orally with NaI125 twice daily for 31 days. From the 11th through the 26th day, 80 mg of L-thyroxine daily were added to dosing capsules for 3 cows, the fourth serving as a control. Although thyroxine lowered milk I125 concentration 15%, this reduction was accompanied by greater milk yield. Total I125 excretion in milk, urine or feces was not change by the thyroxine feeding.