Some Factors Affecting Iodine Secretion in Milk

Abstract

Summary A series of experiments was conducted to study the manner in which iodine enters cows' milk: (a) Eight cows averaging 23.2lb milk daily were paired with their identical twins in later lactation averaging 10.7lb. Iodine 131 was administered intravenously followed by seven-day collection periods; (b) milk secretion was stopped in the left udder halves of eight cows by allowing a 24-hr accumulation of milk, and the right halves were milked prior to intravenous administration of I 131 . Left and right udder halves were milked at 8- and 32-hr intervals thereafter for six days; (c) Iodine 131 was infused into the gland cisterns of six cows after the morning milking. Absorption of administered I 131 from the mammary gland into the blood stream was estimated from the percentage of the dose recovered in the milk during subsequent milkings. Results indicate that iodide passes easily in both directions between the cow's mammary gland and blood, and that it can enter the milk independent of milk secretion. Protein-bound iodine did not appear to transfer between blood and milk in either direction. It is indicated that iodide enters the cow's udder passively (regardless of secretory activity), but that once it is in the milk-collecting spaces, a portion of the iodine is bound in some manner and is not available for resorption. The greater iodine secretion of higher-yielding cows is related primarily to their greater volume of milk.