An essential trace element required for the formation of Vitamin B12 (Cobalamin) which is manufactured by microbial activity in the hind gut of horses. Essential with Vitamin B12, copper and iron for the formation of red blood cells. Also involved in energy metabolism in complexes with other compounds including production of glucose from volatile fatty acids. Cobalt is absorbed in the hind gut as part of cobalamin complexes formed by gut microbes. Where dietary cobalt is deficient the symptoms would be those of Vitamin B12 deficiency. An intake of 0.5 – 0.6mg per day for a 500kg horse is deemed adequate. Cobalt was tried as a performance enhancer following suggestions in lay press that high doses may stimulate erythropoietin (EPO) production and it was used in competitive cycling and then by some horse trainers in 2013. Racing authorities intervened and set pre- or post- race urine levels of 100 micrograms per liter above which the Rules of Racing may be breached. There has been some controversy over what constitute the ‘’normal’’ range of cobalt in the horse population as it can come from a variety of legitimate natural sources. Appropriate care should be taken if using Cobalt containing feeds or supplements in competitive sport / racehorses.