Dietary supplementation of iodine is absolutely essential for livestock due to its critical role in the synthesis of thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3). These hormones are vital regulators of almost every metabolic process in the animal's body.

Thyroid hormones influence:

1. Metabolic Rate: They control the basal metabolic rate, affecting energy utilization and heat production.
2. Growth and Development: Essential for proper growth of young animals, skeletal development, and maturation of the nervous system.
3. Reproduction: Iodine deficiency can lead to reproductive failures, including infertility, stillbirths, weak offspring, and retained placentas in breeding animals.
4. Lactation: It impacts milk production and composition.

A deficiency in dietary iodine leads to hypothyroidism, characterized by an enlarged thyroid gland (goiter) as it attempts to compensate. Other signs include poor growth, dull coats, lethargy, poor reproductive performance, and reduced immunity. Therefore, ensuring adequate iodine intake through fortified feeds or mineral supplements is crucial for optimizing livestock health, productivity, and reproductive efficiency.