Secretion of Radioiodine in Milk Following a Single Oral Administration in the Cow

The secretion of radioiodine in the milk following the administration of a single oral dose was studied using I131. All of the values are corrected for the physical decay of the isotope. I131 began to appear in the milk 30 minutes after administration with a maximal concentration of, on the average, 1.7 per cent of the given dose per 1 of milk at about six hours following administration. The subsequent reduction in the concentration showed a two exponential course with biological half-lives of 0.6 days and 10 days, respectively. The total secretion in the milk was between 10 and 27 per cent of the given dose of I131 in six days. The total secretion of radioiodine in the milk was seen to be dependent upon the cow’s milk production.