Potassium iodide is an ionic compound, in which iodide ions can form dark yellow precipitated silver iodide with silver ions (see photolysis, which can be used to make high-speed photographic film), so silver nitrate can be used to test the existence of iodide ions. As a component of thyroxine, iodine is closely related to the basal metabolism of livestock and poultry, and participates in almost all material metabolism processes. Iodine deficiency in livestock will cause thyroid hypertrophy and hypertrophy, decrease basal metabolic rate, and affect growth and development. Young animals and livestock and poultry in iodine-deficient areas need to add iodine to their feed. High-yielding dairy cows and high-yielding laying hens have an increased iodine requirement, and iodine also needs to be added to their feed. The iodine in milk and eggs increases with the increase of feed iodine. High-iodine eggs have been reported to reduce cholesterol levels in the human body and are beneficial to the health of people with high blood pressure. In addition, during the fattening period of animals, although there is no iodine deficiency, in order to make the thyroid function of livestock and poultry vigorous, enhance the anti-stress ability, and maintain the highest production capacity, iodide is also supplemented, and potassium iodide is added to the feed as an iodine source to prevent iodine deficiency. , to promote growth, increase egg production rate and reproduction rate and improve feed utilization rate, the addition amount in the feed is generally several PPM, because it is unstable, usually add ferric citrate and calcium stearate (generally add 10%) As a protective agent to stabilize it.