Iodine transfer to dairy cow's milk: A revised biokinetic model

A new biokinetic model for iodine in dairy cows was developed utilizing data from a 4 × 4 factorial feeding experiment with rumen-cannulated cows that were fed rapeseed cake containing substances known to influence iodine metabolism, and soybean meal without such effects. ¹³¹I was administered both intravenously and intra-ruminally to document metabolism pathways. The new model included compartments such as saliva and thyroid gland, often ignored in other models, and in contrast to previously available biokinetic models, it fitted well to our experimental data. Compared to cows fed soybean meal diet, rapeseed cake diet resulted in lower retention of ¹³¹I in body compartments, reduced ¹³¹I transfer to milk, and increased urinary excretion of ¹³¹I. Over time, low retention of iodine from diets containing goitrogenic substances like rapeseed would increase the risk of iodine deficiency, in both cattle and humans. Based on sensitivity analysis, milk, blood and liver pathways contributed the most to the model uncertainty. The proposed model should be relevant in elucidating mechanisms governing iodine uptake and metabolism in dairy cows, to predict how feeding can be used to optimize iodine concentrations in milk, and to reduce transfer of radioiodine through dairy products in case of fallout from nuclear events.