Horses in heavy work, along with mares in late gestation and lactating broodmares, require more idoine than the average horse at rest. | Photo: iStock

The trace mineral iodine is regarded by some as one of the most critical dietary trace minerals. This is due to the important role that it plays in the thyroid metabolism and in the synthesis of the thyroid hormones triiodothyronine and thyroxine. These hormones fulfill multiple functions ranging from cell regulation to tissue differentiation and growth. When the body’s iodine status declines to the point that the levels of these hormones become insufficient, the thyroid gland becomes enlarged. This phenomenon is commonly referred to as goiter.

Some of the earliest references to goiter comes from the ancient civilizations of China, India, Greece, and Rome. In particular, a book of Chinese origin dating back to 2000 BC, referenced the use of seaweed against goiter. Iodine was discovered in 1811 and, following the detection of iodine in seaweed, a Swiss physician made the connection and started treating patients suffering from goiter with iodine solutions around 1820.

Globally, almost all countries have been affected by iodine deficiency disorders at some point in time. In part this relates to the fact that soil iodine concentrations tend to be low in general; this is often reflected in plant iodine concentrations. Therefore, iodine deficiencies tend to be more prevalent than toxicity in unsupplemented grazing animals