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Iodine Toxicity: Physiological Effects of Elevated Dietary Iodine on Pigs^{1, 2,}

North Carolina State University Raleigh 27607

Abstract

Three trials were conducted to study the effects of elevated dietary iodine (calcium iodate) intake on the performance, thyroid gland development, liver iron concentration and certain blood constituents in pigs. No differences in performance measures were noted at iodine levels of 400 ppm or lower; however all levels of added iodine increased serum iodine levels and thyroid gland weights. The feeding of diets containing 400 to 1,600 ppm added iodine significantly depressed liver iron concentration. Growth rate, feed intake and hemoglobin levels were depressed when pigs received diets containing either 800 or 1,600 ppm added iodine. Dietary and intramuscularly injected iron tended to offset the effects of iodine on growth rate and feed intake. Iron, either added to the feed at an equivalent level with iodate, or injected at the calculated physiological requirement, maintained hemoglobin levels significantly above those of pigs receiving only iodine. There was no apparent effect of supplementary iron on serum iodine level.

In growing-finishing swine the minimum toxic level of iodine from calcium iodate appears to be between 400 and 800 ppm. However, if the depression in liver iron at added dietary iodine levels of 400 ppm and above is considered, the minimum toxic level over extended periods may be below 400 ppm.

¹ Paper No. 4256 of the Journal Series of the North Carolina State Agricultural Experiment Station, Raleigh, N. C. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of the products named, nor criticism of similar ones not mentioned.

² Acknowledgement is given to Morton Salt Company, Chicago, Illinois for supplying the calcium iodate.

³ Present address: Department of Animal Science, Coastal Plain Experiment Station, Tifton, Georgia, 31794.