Chronic iodine toxicity in dairy cattle: blood chemistry, leukocytes, and milk iodide

Preliminary data from farm herds fed excessive dietary iodide and displaying signs of iodism indicated hyperglycemia, hypocholesterolemia, and a neutrophilic-lymphopenic shift in blood leukocytes. Subsequently blood, milk, and urine were analyzed from 90 cows in 10 herds fed normal (average 16 mg/cow daily) or high (average 164 mg) iodide as ethylenediamine dihydriodide for prophylactic purposes and from one herd fed iodinated casein for 3 wk. Glucose, area nitrogen, and neutrophils were higher while cholesterol and lymphocytes were lower in blood from cows fed high iodide. Milk iodide averaged .37 +/- .03 ppm from normal and 2.16 +/- .25 from herds fed high iodide. Neutrophils, glucose, protein, and globulin of serum increased while lymphocytes, cholesterol, and thyroxine decreased as iodide in milk and urine increased. Signs of iodism included lacrimation, coryza, conjunctivitis, coughing, hair loss, and exophthalmus. These findings corroborate other reports that excessive iodide alters metabolism and is toxic to immune mechanisms, suggesting that dietary iodide should be limited to nutritional requirements and prolonged prophylactic or therapeutic use should be avoided.