Some Factors Affecting Iodine Secretion in Milk

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Abstract
A series of experiments was conducted to study the manner in which iodine enters cows milk: iodinel31 was administered to eight cows averaging 23.2 lb milk daily and their identical twins in later lactation averaging 10.7 lb; milk secretion was stopped in the left udder halves of eight additional cows by allowing a 24-hr accumulation of milk prior to intravenous administration of I131 after which left and right udder halves were milked at 8- and 24-hour intervals; and I131 was infused into the gland cisterns of six cows after the morning milking. The results indicate that iodide passes easily in both directions between the cows 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 cows 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.