Folic Acid is the synthetic form of naturally occurring Folate which is required for the synthesis of DNA, purine, and the amino acid Methionine. It is therefore in highest demand in tissues undergrowing rapid cell division like bone marrow and gut lining cells.
Folate levels in fresh forage are higher than in preserved forages like hay or grains but folate deficiency has never been reported in the horse as folic acid is manufactured by the gut microflora in sufficient amounts to meet normal requirements. Whilst no dietary requirement has been established for folate it is possible that levels may become undesirably low when horses have no access to fresh forage for prolonged periods e.g., racehorses which may have increased demand due to intense exercise, or in lactating mares. For this reason, adding small amounts of folic acid to manufactured feeds is common practice.