Cobalt's importance is entirely as an essential component of vitamin B12, formed by rumen organisms and absorbed, with the aid of gastric intrinsic factor, from the ileum.
This is probably the most economically important of the ruminant trace deficiencies, particularly in cattle.
Iodine is required for synthesis of the thyroid hormones, thyroxine (T3) and tri-iodo thyronine (T4). Deficiency, in extreme cases, results in goitre. Deficiency is generally regarded as being most likely where humus content of soil is low, and where rainfall is heavy. High calcium intake reduces iodine absorption. Brassicas can precipitate deficiency, through supplying goitrigeric substances such as thiocyanate.
Selenium is a necessary component of glutathione peroxidase, whose known function is to minimise oxidative tissue damage. Challenge is greatest at times of greatest intake of polyunsaturated fatty acids, for example when grazing rapidly growing spring grass.
