Iodine is a trace mineral essential for the production of thyroid hormones (T3 and T4), which regulate metabolic rate, body temperature, and the growth cycles of feathers and other tissues. In laying hens, thyroid hormones influence the timing and intensity of the annual molt, the rate of egg production, and the ability to maintain body condition through seasonal changes.
The thyroid gland concentrates iodine from the blood at levels 20 to 30 times higher than other tissues, making it the body's most iodine-dependent organ. When dietary iodine drops below adequate levels, the thyroid enlarges (goiter) as it struggles to produce enough hormone from limited raw material. Goiter in chickens appears as a visible swelling in the neck area.
Iodine content in feed depends heavily on the iodine content of the soil where feed crops were grown, which varies significantly by region. Coastal areas tend to have iodine-rich soils, while inland and mountainous regions may be deficient. Most commercial feeds add iodine (typically as calcium iodate) to ensure adequate levels regardless of regional soil variation.
Laying hens need about 0.3 to 0.5 mg of iodine per kilogram of feed, which commercial feeds provide. Kelp meal is a popular natural supplement among backyard keepers, but use it sparingly â a small pinch per hen a few times per week rather than daily, as kelp is very concentrated in iodine and excess is counterproductive. In iodine-poor regions, ensure your feed includes an iodine source.
0.0% of daily nutrient intake
Iodine makes up 0.0% of your chicken's total daily nutritional requirements by weight. That's a tiny amount â but it matters.
Enlarged thyroid gland visible as a swelling in the neck (goiter), reduced egg production, prolonged or incomplete molt, poor cold tolerance, lethargy, slow growth in young birds, reduced hatchability of fertile eggs
Iodine toxicity reduces egg production and causes a decrease in egg weight. Excessive iodine can interfere with thyroid function paradoxically, suppressing hormone production. Very high levels cause reduced feed intake, watery droppings, and in severe cases organ damage. Avoid feeding excessive kelp or seaweed supplements.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | â | 0.3 | 0.5 | mg/kg feed | Essential for thyroid hormones that regulate metabolic rate and molt timing. Soil iodine varies by region. Use kelp sparingly as it concentrates iodine. |
Source: NRC Poultry 1994; Merck Veterinary Manual
