Iodine and Animal Health

Iodine is an essential trace mineral critical for animal health, primarily due to its role in the synthesis of thyroid hormones—thyroxine (T₄) and triiodothyronine (T₃)—which regulate metabolism, growth, reproduction, and thermoregulation. 

• Deficiency leads to goiter (thyroid gland enlargement), reduced growth, poor fertility, impaired lactation, weakened immunity, and fetal developmental issues.  Regions with iodine-deficient soils (e.g., Great Lakes and Northwest U.S., parts of Canada) pose higher risk, especially when relying on local forages.

• Toxicity from excessive iodine intake (e.g., overuse of supplements) can cause iodism—marked by cough, nasal discharge, dermatitis, weight loss, and increased mortality, particularly in dairy cattle and sheep. 

• Iodine is efficiently absorbed (70–80%) in the rumen and intestines and is concentrated in the thyroid, milk, and eggs—making animal-derived foods a significant source of iodine for humans. 

Proper iodine management ensures animal productivity, food safety, and human nutrition. 

Iodine is an essential trace mineral required by horses and all mammals. It is used to make thyroid hormones that control metabolism in all cells of the body. Horses need about 3.5-4 mg of iodine daily.

Forages and grains are typically low in iodine because most soils have low concentrations of this mineral. Horses that do not get enough iodine in their diet can develop subtle signs of deficiency including dry skin, dull coat, poor appetite and low stamina.

Foals are most at risk of iodine deficiency or excess. Foals born to mares that consume too much or too little iodine can experience growth abnormalities and general weakness. 

The classic sign of iodine deficiency is goitre – an enlarged thyroid gland. However, only a few cases of severe iodine deficiency have been reported in horses.

Iodine excess in the diet can also cause thyroid dysfunction and lead to similar symptoms. Horses showing signs of thyroid dysfunction should have their iodine status and levels of thyroid hormones evaluated.

Optimal supplementation is key: National Research Council (NRC) recommends 0.2–0.3 ppm for dairy cattle and 0.33 ppm for beef cattle.  For pigs and beef cattle, 120–250 μg/kg dry matter is advised to maintain performance and thyroid function