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When it comes to horse nutrition, it’s vital to remember that no mineral, vitamin, or electrolyte works in isolation. Inside your horse’s body, thousands of complex biochemical reactions are constantly taking place. These reactions involve intricate interactions between minerals, vitamins, electrolytes, proteins, and energy sources. While science has answered many questions, there are still areas of horse nutrition that remain unclear. However, an observant and educated horse owner can often assess their horse’s health, performance, and appearance which are reliable reflections of the diet being fed.
Iodine is a trace mineral, meaning it's required in very small amounts. However, both deficiency and excess iodine can cause significant health problems in horses, making it crucial to get the balance right. Why Do Horses Need Iodine? Iodine plays an essential role in the thyroid gland, where it’s used to produce the hormones thyroxine (T4) and triiodothyronine (T3). These hormones are critical for regulating your horse’s metabolism, growth, body temperature, and overall energy levels.
Interestingly, both iodine deficiency and iodine excess can cause similar symptoms, such as:
Iodine content in feeds can vary greatly depending on the iodine levels in soil. While most plant matter contains anywhere from 0 to 2 mg of iodine per kg of dry matter, some types of kelp can contain as much as 1,850 mg/kg.
Additional iodine sources include:
The recommended iodine requirement for horses is approximately 0.1 to 0.6 mg per kg of dry matter intake. For a 500 kg horse eating 10 kg of dry matter daily, this equates to:
Horses are generally very efficient at absorbing, storing, and utilising iodine, especially given its limited availability in natural feeds. However, some horses may still be at risk of deficiency, particularly if they rely solely on iodised salt and have increased needs due to age, pregnancy, or underlying health issues like Cushing’s Disease.
Directly measuring iodine levels in horses is difficult. Instead, veterinarians often assess T3 and T4 hormone levels as indicators of iodine status. If your horse develops a goitre or shows signs of thyroid dysfunction, it’s essential to review their overall health and diet. Certain horses such as aged ponies, pregnant mares on poor diets, or horses with metabolic disorders such a Cushings may show symptoms even when dietary iodine appears adequate.
Iodine is a small but vital part of a balanced equine diet. Whether you're feeding a performance athlete, a broodmare, or a pleasure horse, make sure iodine intake is appropriate, not too little, not too much. Monitoring your horse’s condition and working with your vet or equine nutritionist will help you make informed decisions for long-term health and performance.
