Results of Prolonged Increased Iodine Feeding

Abstract

The advisability of adding iodine to the diet of man and animals has long been questioned. The herd of Brown Swiss dairy cows at the farms of Mr. William Wallace Kincaid,∗ Ellerslie-on-Niagara, New York, had been fed daily large amounts of iodine during a period of 2 years and 11 months. They were, consequently, satisfactory experimental animals for investigating the effects of prolonged increased iodine feeding. The blood iodine was of particular interest. The normal bovine blood iodine is 13, 1 or 14 2 gamma %. In 19 cows of this herd the blood iodine ranged from 35.9 to 78.1 gamma %, averaging 55.

Analyses of the feed given these cows daily, revealed the increased iodine intake (Table I). Since the high milk producing cows were fed more of the “grain mix” they ingested greater amounts of iodine (Table I, a). The natural iodine content of the “grain mix” had been increased by the addition of potassium iodide, fish meal, and kelp. The iodine content of this thoroughly mixed food was 2.006 mg. per 100 gm. The daily iodine intake of the cows varied from 68.6 to 196.1 mg.

Large amounts of iodine, from 51.7 to 163.4 mg. daily, were eliminated, Table II. More was eliminated in the urine than in either the milk or the feces. The high milk producing cows likewise showed the greater elimination of iodine, (Table II, a).

The milk iodine was increased. It ranged from 15.7 to 181.9 gamma per 100 cc, averaging 66.4. The average iodine content of milk from cows on usual feed is 5 gamma per 100 cc. 2 , 3

All physical examinations showed the cows to be in very good general condition. Cows of the herd previously sterile have become pregnant and borne normal calves during this regimen of feeding.