Influence of an iodine depletion period and teat dipping on the iodine concentration in serum and milk of cows

The objectives of the study were to investigate the influence of an iodine depletion period (from 10 to 0.2 mg I per kg dry matter, DM) on the iodine concentration of serum and milk and the effect of an iodized udder disinfectant solution on the iodine concentration of milk from dairy cows. Five late-lactating cows (milk performance: 22.1 +/- 2.0 kg per day) were used for the study. At the end of the dose-response study (up to 10 mg I supplementation per kg DM) without teat dipping, the basal diet (0.2 mg I/kg DM) was given for 16 days. The serum iodine concentration decreased from 290 to approximate to 60 mu g kg(-1), that of milk, from 2762 to approximate to 100 mu g kg(-1). In the second part of the study the teats were separately dipped twice a day after milking in a disinfectant providing a free available iodine concentration of 3 g per l through nonoxinol(9)-iodine. The diet fed had a native iodine content of 0.2 mg/kg DM. Dipping was compared over 18 days with non-dipping. The dipping procedure significantly increased the mean iodine concentration from 100 +/- 23 to 154 +/- 42 mu g kg(-1) milk.