Factors Affecting Iodine Concentration of Milk of Individual Cows

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Abstract
Variations were measured of I concentrations of milk during complete lactations of 36 Holstein cows from the Univeristy of California [USA] herd in Davis and 24 Holstein and 12 Guernsey cows from the California State University herd in Fresno. At Davis no I was added to the concentrate; at Fresno I as ethylenediamine dihydroiodide was added to the concentrate at 4 ppm. At Davis, the mean milk I concentration was 166 .mu.g/kg; at Fresno, the mean milk I concentration was 745 .mu.g/kg. Holstein milk had higher I concentrations than Guernsey milk, 839 vs. 554 .mu.g/kg. I concentrations of milk increased during lactation for all cows. At Davis, samples taken in the 1st mo. of lactation had 105 .mu.g/kg compared with 218 .mu.g/kg in the 9th mo. At Fresno, samples taken in the 2nd wk of lactation had 183 .mu.g/kg, compared with 1017 .mu.g/kg in the 40th wk. Addition of as little as 4 ppm ethylenediamine dihydriodide to the concentrate throughout lactation will lead to greatly increased I concentrations in the milk, particularly in late lactation.