Performance and Iodine Metabolism of Dairy Cattle With Iodine131 Irradiation Injury

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Abstract
Four mature cows and 6 growing heifers were given single oral doses of 190-220 [mu]c I131/kg body wt after preliminary measurements of thyroid I131 uptake, thyroid secretion rate, and metabolism of daily tracer levels of I125. Radiation doses to the thyroids were calculated as 12,000 to 27,000 rad. One cow and the identical twins of the 6 heifers were used as controls. Within 10 days, blood plasma I125 concentrations of I131 treated heifers abruptly rose to 3 times control values then dropped sharply. The elevated plasma I125 levels, most likely from release by damaged thyroids of previously stored I125, were accompanied by increased urinary and fecal I125 excretions. Thyroid activity 6 mo. later was reduced as shown by average decreases of 64% in plasma protein-bound iodine, 80% in thyroid I131 uptake, and 56% in thyroid secretion rate. Three cows calved 15, 123, and 136 days after each had received 100 mc of I131. The 15-day calf was a cretin with no detectable thyroid activity, the 123-day calf died just after birth, and the 136-day calf was apparently normal. Surviving animals exhibited varying degrees of hypothyroidism 6 mo. after treatment. Low milk yields of the lactating cows and growth of the cretin calf were improved by feeding iodinated casein.