The effects of iodised salt licks and teat dipping on the iodine content of cow's milk and blood plasma

Milk has been identified as the ideal carrier of iodine in the human diet. The iodine concentration in cow's milk depends on the iodine intake in the animal's daily rations. The first experiment, which lasted for 90 days, investigated the effectiveness of salt licks containing 0 (control group), 150, and 300 mg I/kg (experimental groups) and the effect on the iodine content of cow's milk and blood plasma. The second experiment determined the effect of udder disinfection and iodine teat dipping with iodine disinfectant (experimental group) compared to chlorine dip (control group) on the iodine content of milk and blood plasma. Milk iodine and blood plasma concentrations were meas- ured using the Sandell-Kolthoff method modified by the Bobek and Kołczak procedure. Salt licks containing 150 and 300 mg I/kg increased iodine intake by 7.5 and 15.0 mg I/day, respectively. Average iodine intake in the control group was 6.23 mg I/day, and 13.68 and 21.10 mg I/day in the experimental groups, respectively. There were no significant differences in the average cows' milk yield, which averaged 21.0 ± 1.1 kg/day. Average milk iodine content was 53.8 μg/1000 mL (control group), 65.0 and 84.7 μg/1000 mL (experimental groups). Average plasma iodine content tended to increase in the experimental groups, but the differences between the groups were not significant. In the second experiment iodine udder disinfection and teat dipping increased average milk iodine content from 44.0 ± 1.6 to 59.3 ± 2.3 μg/1000 mL. Average plasma iodine content increased only slightly, with a non- significant difference between the control and experimental groups. The iodine content of salt licks at 150 and 300 mg I/kg makes it possible to obtain from 65 to 85 μg I/1000 mL of cow's milk. Pre-milking udder hygiene and post-milking iodine teat dipping additionally increase the iodine content of milk by around 15 μg I/1000 mL milk, i.e. an increase of 35% in relation to cows from the control group.