Vitamin A is a vitamin with many functions that affect just about every system of the body. In the past we have known little about its function in horses so we surmise from work done in other species. Recent work on blood levels during different conditions suggests we should pay more attention to this vitamin.

Vitamin A is naturally ingested as its precursor form called carotenoids. Only about 9% of the known carotenoids can be used by the body to make vitamin A with beta-carotene is the most useful of the carotenoids. The richest source of carotenoids is fresh green forage. Lon Lewis states in his book on clinical nutrition of the horse that hay with any green in it and constituting at least 50% of the diet, should provide adequate amounts of vitamin A and vitamin E. Hay after it is baled and kept in good conditions loses about 9% of its carotenoids every month. This has been the belief for sometime and I know of no-good reason to change it. However in the Jan 98 World Equine Review it is stated: Cutting and baling destroys about 80% of the carotenoids that then decrease by 7% a month thereafter. Horses with only hay available probably will require supplementation to maintain body levels.