Chronic Iodine Toxicity in Dairy Cattle: Blood Chemistry, Leukocytes, and Milk Iodide

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Abstract
Preliminary data from farm herds fed excessive dietary I- 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) I- as ethylenediamine dihydriodide for prophylactic purposes and from 1 herd fed iodinated casein for 3 wk. Glucose, urea nitrogen, and neutrophils were higher while cholesterol and lymphocytes were lower in blood from cows fed high I-. Milk I- averaged 0.37 .+-. 0.03 ppm from normal and 2.16 .+-. 0.25 from herds fed high I-. Neutrophils, glucose, protein and globulin of serum increased while lymphocytes, cholesterol, and thyroxine decreased as I- in milk and urine increased. Signs of iodism included lacrimation, coryza, conjunctivitis, coughing, hair loss and exophthalmus. These findings corroborate other reports that excessive I- alters metabolism and is toxic to immune mechanisms, suggesting that dietary I- should be limited to nutritional requirements and prolonged prophylactic or therapeutic use should be avoided.