For many of us, iodine is the yellowish-brown liquid that we put in the first-aid kit and is used to treat horses when they get injured. And it is indeed true that povidone-iodine is commonly as a skin antiseptic. But a less known fact is that iodine is a vital trace mineral that should also be included in the horse’s diet.
In the body, this important mineral is mostly found in the thyroid gland which is positioned near the trachea and just behind the voice box (also called the larynx). It plays an instrumental role in the production of triiodothyronine (T3) and thyroxine (T4), both of which are thyroid hormones that regulate the body’s metabolic processes.
Recommended iodine requirements and sources
A study conducted by the National Research Council on the subject of the recommended nutrient requirements of horses (and whose results were published in a 2007 report) found that a normal adult horse, weighing in at 500 kilos (or 1100 pounds) needs between 3.5 and 4.5 milligrams of iodine in his diet every day. But again this depends on the horse's breeding status and exercise schedule.
There is little available information in regards to the concentration of iodine in ordinary forages due to the fact that it is not commonly measured when doing sample analysis. Using iodized salt is a simplified method of supplementing the mineral. It is also contained in various horse feed such as whey, molasses, kelp, alfalfa meal and kelp.
Causes and symptoms of iodine deficiency and toxicity in horses
One typical symptom of both iodine toxicity and deficiency is the enlargement of the thyroid gland commonly referred to as a goiter. Iodine deficiency is generally manifested as a lack of appetite, lethargy, intolerance to cold, hair loss (or dull coat) and thickening of the skin. Among foals, deficiency of the mineral is expressed as being born weak or stillborn, developing hypothermia, poor response to suckling and experiencing difficulties when standing. If it is not rectified, iodine deficiency can cause various problems in the working of multiple organs and orthopedic disease when the horse is developing.
There is a possibility of a horse suffering from the problem iodine toxicity due to over-supplementation. It is interesting to note that a goiter can also develop due to excessive intake of the mineral. Signs that a horse has consumed excess iodine include low-grade fever, frequent eye tearing, increased susceptibility to infections, a nasal discharge that is unresponsive to treatment and having a high probability of developing chronic respiratory complications.
The bottom line
Whereas it is required in very minute quantities, iodine is essential for a horse’s proper growth and development, healthy metabolism and general health. Since it is not usually measured when conducting analyses of the forage or hay, it is not easy to do an approximation of the iodine concentration in these feeds without precisely testing for it. The majority of commercial grain preparations are fortified with this important mineral. For horses that consume diets comprising of forage only, an iodized salt block is an easy method of ensuring sufficient intake of the essential trace mineral.
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