The name covers a group of Cobalt containing cobalamins which are synthesised in the hind gut by the microbiota. Vitamin B12 is important in energy metabolism and as a supplier oof Cobalt, in several other processes and proteins. The liver is the most important site of B12 metabolism, and the main route of excretion is in the bile. The supply of B12 produced by intestinal microbes is adequate to meet requirements and dietary input is unnecessary. Deficiency has not been reported in horses and even when cobalt intake is extremely low there appears to be sufficient to maintain adequacy of this vitamin. A minimum cobalt requirement has been set by NRC at 0.1 mg/kg Dry Matter of feed which is easily met by most forage feeds with Lucerne being a good source.
Supplements of B12 are widely thought to stimulate appetite and enhance red blood cell production but hard evidence for this is lacking and indeed, any supplementary B12 which is administered either orally or by injection is cleared from circulation into the bile very rapidly.