Trace Mineral Basics: Iodine

By Nettie Liburt,
 MS, PhD, PAS

When we think of iodine, most of us think of the dark yellowish-brown liquid in the first-aid kit we might use to treat our horses’ wounds. Indeed, povidone-iodine is a common skin antiseptic. But iodine (I) itself is actually an important trace mineral in the horse’s diet.

Iodine is concentrated in the thyroid gland, located next to the trachea and behind the larynx (voice box). It is essential for the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which regulate the body’s metabolism.

Requirements & Sources

According to the National Research Council’s Nutrient Requirements of Horses (NRC), 2007 edition, an average mature 1,100-pound (500-kilogram) horse requires a minimum of 3.5-4.5 milligrams of dietary I per day, depending on exercise regimen and breeding status.

Little information is available regarding iodine concentration of common forages, because it’s not usually measured in sample analyses. Iodized salt is a simple way to supplement I. Molasses, alfalfa meal, whey, algae, and kelp also contain I.
 

Deficiency and Toxicity

Goiter, an enlargement of the thyroid gland, is a classic symptom of both I deficiency and toxicity. General signs of deficiency include lethargy, dull coat/hair loss, lack of appetite, thickened skin, and cold intolerance. Deficient foals can be stillborn or born weak, have hypothermia, difficulty standing, and a poor suckle response. If not corrected, I deficiency can lead to developmental orthopedic disease and problems in multiple organ systems.