ae? Reprinted from JourNaL oF Dairy SCIENCE, February, 1965, Vol. XLVIII, No. 2, pages 197-202 FACTORS AFFECTING IODINE CONCENTRATION IN BOVINE MILK! Ke F. W. LENGEMANN Department of Physieal Biology, New York State Veterinary College,. Cornell University Ithaca, New York ABSTRACT | The purpose of this study was to investigate the effect upon the secretion of iodine into cows’ milk of various compounds demonstrated to alter thyroid 407943 funetion. Nine cows were given radioiodine twice daily to achieve a steady state condition. After a control sampling period the cows were given KC10,, NaI, NaCl, and .-thyroxine, p-thyroxine, or 2-4 dinitrophenol. KC10,, Nal, NaCl, and u-thyroxine reduced the accumulation of radioiodine in milk and reduced the milk-I/plasma-I™ ratio; whereas, p-thyroxine and 2-4 dinitrophenol did not. L-thyroxine, although probably acting directly upon the mammary gland, was limited in its ability to reduce I accumulation in milk. It was concluded that transfer of iodide into milk was in part an active process and that thyroxine could affect the transfer of iodide from plasma to milk and from milk to plasma. The transfer of iodine across the mammary gland has been of interest to many investigators over the years and interesting observations have been made. The ability of the mammary gland to concentrate iodine has been observed (using laboratory animals) to bear a marked similarity to the iodide concentration mechanism of the thyroid (2). In both glands anions such as thiocyanate, nitrate, perchlorate, and excess iodide interfere with concentration of iodide. Compounds that block thyroid fune- tion hy affecting the binding of iodine in or- ganic complexes do not, however, seem to affect the iodide-concentrating mechanism of the mammary gland. Further information is needed to determine if the iodide-conecntrating imechanism in the mammary gland is identical with that of the thyroid. While the mammary iodide-coneentrating mechanisms are likely to be similar in laboratory animals and large ruminants, quantitative differences may exist that may make it more meaningful to examine miuk secretion in species kept primarily for milk production. The recognition that radioiodine from fallout enters the food chain of man through milk provides an additional reason for using economically important species. It was with these points in mind that the present experiments were done on the transfer of iodide from plasma to milk. Whereas these Received for publication June 5, 1964. studies represent a gross approach to the subject, they can serve as a basis for more precise studies on how iodine is secreted into the milk of dairy animals. METHODS A total of nine milking cows was used for this study; in several instances a particular cow The old, had was used for more than one experiment. animals were from three to seven years had no diseases, were not pregnant, and been milking at least four months. Five of the cows, three Guernseys and two Holsteins, were purchased from local farms and weighed from 370 to 425 kg. The four other cattle were Holsteins raised at the laboratory, weighing from 500 to 600 kg. During the experimental period the animals were fed from 4.6 to 9.2 kg of a eommercial dairy ration (18% protein) and all the mixed orchard grass—alfalfa hay they would eonsume. Milking, feeding, and radioiodine administration were done at 8 am and 4 pm every day. The animals were confined in metabolism stalls to facilitate collection of samples and were given an I™ capsule per os after each milking during the experiment. This capsule was prepared by pipetting 0.5 ml of an alcoholie solution containing about 100 ue of KI™ (carrier-free) into a gelatin capsule, then drying under low heat. All capsules were prepared before the start of an experiment. Taking of samples began after the animals had received I™ for seven days. *This work was supported in part by USDA Contract 12-14-100-2599(45) and U.S, AEC Contract AT 30-1-2147. Milk was collected at each milking; blood samples were taken and thyroid counts made about 10 am each day. In some instances urine and feces (1].