Iodine in California Farm Milk: 1985-1986 ¹

Iodine has been measured in 1572 California farm milk samples, representing 2,725,000 gallons of milk, or about 54% of daily production. The mean iodine concentration in the analyzed samples was 173.3 μg/kg milk, with a standard deviation of 115.8 μg/kg- The volume-corrected mean iodine concentration for all samples was 188.3 μg/kg. Of the farms examined, 13% used neither an iodine teat-dip or backflush; the milk iodine concentration on these dairy farms averaged 147.8 ± 90.2 μg/kg. Of the farms examined, 73% used iodine teat-dip only; milk iodine concentrations averaged 166.7±109.4 μg/kg. Less than 1% of the farms used iodine only in their backflush systems; their milk iodine concentrations averaged 202.3±107.2 μg/kg. Thirteen percent of the farms used both iodine teat-dip and iodine in their backflush systems; their milk iodine concentrations averaged 251.3±153.9 μg/kg. While the concentration difference between farms using iodine in both the teat-dip and backflush system and farms in the other three groups was statistically significant, the mean concentration was still well below the maximum limit of 500 μg/kg imposed by health agencies in some countries. Overall, 30.7% of samples measured has less than 100 μg iodine/kg; 70.1% had less than 200 μg/kg; 88.8% had less than 300 μg/kg; 94.4% had less than 400 μg/kg; and 98.1% had less than 500 μg/kg.