Iodine is essential for animals and is present in tissues (0.1 micrograms per gram body weight), but concentrated in the thyroid gland (400 micrograms per gram body weight). The main role of iodine is as a component of thyroid hormones (tri-iodotyronine and tetra-iodotyronine [thyroxine], which are synthesised in the thyroid gland using iodine extracted from the blood-stream. Iodine-containing thyroid hormones regulate metabolism and maintain body functions (body temperature, growth and development, milk production and reproduction).
Iodine deficiency rapidly leads to a reduction in thyroid hormone synthesis, so that the bodily functions controlled by such hormones are less effective. For example stock born from mothers with an iodine deficient diet have the following symptoms: Calves, lambs or piglets may be stillborn, or very weak at birth. Affected breeding poultry lay fewer eggs with poor hatchability, hatched chicks are small and weak. In addition to the above effects, iodine deficiency is visibly indicated by a swollen thyroid gland, or goitre.
Main sources Calcium iodate anhydrous Sodium iodide

Potassium iodide

Quality  and selection parameters
Animals absorb iodine (in the form of iodides) from digested feed in the small intestine, where it is transferred to the blood. Iodine absorption is close to 100 % efficient from inorganic iodine salts or from organic iodine compounds. Iodate salts are stable during storage and the iodine content of feed will remain unchanged with time; thereby ensuring that the animal will receive the required dose of iodine (40 mg/kg of feed) from its feed.
Sodium and potassium iodides lose iodine very rapidly when in contact with other minerals, or in a moist atmosphere. The physical properties of these two iodides cause absorption of water that binds the crystals together, forming lumps that are a major disadvantage when blending together a feed formulation.
The fine crystals of iodate salts have an attraction, similar to that of flour, that need to be overcome in order to generate a free-flowing powder. Inclusion of approximately 0.1 % of an anticaking agent is sufficient to overcome this attraction and to produce an iodate that is free flowing and easy to blend.
Iodide salts are stabilised by addition of stearates that act as a barrier between the crystals and air-borne moisture. This additive is intended to prevent decomposition to release iodine and maintain free-flowing properties.
Analytical methods
Iodine content - salt dissolution followed by thiosulphate
    titration with starch indicator
Assay - calculated by stoichiometry