Performance and Iodine Metabolism of Dairy Cattle With Iodine131 Irradiation Injury

Four mature cows and six growing heifers were given single oral doses of 160-220 t~c I ~ kilogram body weight after preliminary measurements of thyroid I ~a uptake, thyroid secretion rate, and metabolism of daily tracer levels of 11~.Radiation doses to the thyroids were calculated as 12,000 to 27,000 rad.One cow and the identical twins of the six heifers were used as controls.Within ten days, blood plasma I ~ concentrations of I~-treated heifers abruptly rose to three times control values, then dropped sharply.The elevated plasma I ~ levels, most likely from release by damaged thyroids of previously stored V ~, were accompanied by increased urinary and fecal F ~ excretions.Thyroid activity six months later was reduced, as shown by average decreases of 64% in plasma protein-bound iodine, 80% in thyroid I ~ uptake, and 56% in thyroid secretion rate.Three cows calved 15, 123, and 136 days after each had received 100 me of I ~1.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 six months after treatment.Low milk yields of the lactating cows and growth of the cretin calf were improved by feeding iodinated casein.Among potential hazards associated with chemical processing of materials containing fission products and the operation of nuclear reactors is the accidental release of radioactive gases or vapors into the atmosphere.Radioiodine is one of the principal biologically important elements released.Grazing cattle may consume considerable I ~ because of the relatively large land area they graze.Intakes of 11~ which could produce injury to cattle exceed the doses that would render animal products (milk) unfit for human consmuption (3).However, milk would be acceptable for use within a few weeks after consumption of radio-Received for publication August 8, 1966.iodine-contaminated feed by lactating cows, due to rapid excretion (9) and physcial decay.It then becomes of interest to determine the effects of such exposure on later production and health of cattle.Chronic radioiodine injury" has been studied extensively in sheep (2, 12).Garner et al. (4) reported the effects on mature, nonpregnant, lactating cows of 14 daily 11~1 doses ranging up to a total of 140 inc.In the present report, high levels of 11~ were administered as single doses to mature cows in varying stages of gasration and to nonpregnant, growing heifers.Tissue damage in iodine-concentrating organs could result in altered iodine metabolism.Thus, metabolism of dietary iodine, simulated by daily orally administered 11"~, was measured before, during, and after exposure to the high 1181 level.