Effects of dietary iodine supplementation and post-milking teat dip on milk iodine and plasma metabolites in lactating Holstein cows fed a canola-based ration

Dairy products, especially the intake of dairy products by children, are quantitatively important iodine sources in Denmark, and concerns have been raised relative to the iodine intake of children. The present study investigated two dietary iodine levels, three post-milking treatments (with and without iodine) and compared two milking procedures for effects on blood and milk variables. Six early lactating dairy cows with permanent indwelling catheters were used. Higher urinary iodine concentrations and a tendency for higher blood plasma iodine concentrations were observed with higher iodine supplementation. Milk iodine concentrations remained relatively low with both treatments, below 100 µg/kg. Blood plasma iodine concentrations were higher when the post-milking iodine spray was used. The milking procedure had a small numerical effect on milk iodine when a post-milking barrier product was applied. Dairy cows fed canola-based diets have a low iodine status even when supplemented according to the highest dietary iodine concentration recommended by EFSA.