Fission products and the dairy cow III. Transfer of ¹³¹iodine to milk following single and daily dosing

Abstract

1. The transfer of 131 I to milk has been studied in dairy cows following oral administration of carrierfree material in single doses as sodium iodide or as elementary iodine and in daily doses as sodium iodide. 2. The total recovery from milk during the 6 days following administration of a single dose in twentyeight experiments on fifteen animals ranged from 1·3 to 19·4% of the dose with a mean value of 5·5%. The variations in recovery can be attributed largely to differences in the milk yield. 3. There was no significant difference in the biological availability of 131 I administered as iodide or iodine. 4. The change in concentration of 131 I in milk with time following daily dosing did not follow the predicted course, a peak value being observed in most animals after 1–3 days, followed by a fall and a subsequent rise to a steady value lower than was expected. 5. The presence of a concentrating mechanism in the udder has been demonstrated by administration of sodium thiocyanate. Comparison of the milk total 131 I: plasma dialysable 131 I ratio at different times of the year indicates that the concentrating ability may be lower in the summer than in the autumn-spring months.