 Cobalt is essential to the metabolism of all animals . It is a key constituent of cobalamin , also known as vitamin B12 , the primary biological reservoir of cobalt as an ultratrace element . Bacteria in the guts of ruminant animals convert cobalt salts into vitamin B12 , a compound which can only be produced by bacteria or archaea . The minimum presence of cobalt in soils therefore markedly improves the health of grazing animals , and an uptake of 0 @.@ 20 mg / kg a day is recommended because they have no other source of vitamin B12 . 
