McTarnahans Iodide Powder Horse Supplement, 20-lb bucket; The McTarnahans Iodide Powder Horse Supplement offers iodine supplementation for horses. This supplement can help to correct nutritional deficiencies that result from issues like thyroid conditions. A palatable dextrose base helps to ensure that even picky eaters clean up this supplement, and the formula is ready to use with no pre-mixing needed. Powdered iodine nutritional supplement for horses. Helps to correct nutritional deficiencies that can be caused by issues like thyroid conditions. Palatable dextrose base to appeal even to picky eaters. Ready-to-use formula with no pre-mixing required. Made in the USA.