Cattle will generally self-regulate their intake. Simply put a container in a paddock and fill it with 1kg for every 50-100 animals in the paddock. If the animals are deficient in Iodine, they will consume it quickly but as their Iodine levels rise they will eat less.
Reported Health Benefits
Improved immune system
Improved conception rates, more live births, healthier offspring
Improved animal condition and fatter animals
Improved feed efficiency
Improved milk yield
Reduced incidence of mastitis, milk fever