Your Horse and B Vitamins

Todays horse owners are no doubt aware of the importance of vitamins in the diets of their horses but many may not be aware of the role vitamins play in equine nutrition. Vitamins in their fresh natural form are organic substances found in grains and forages. They are important as cofactors or facilitators for different metabolic function and deficiencies of them can cause disease conditions. Vitamins unlike many of the nutrients we feed our horses cannot be broken down for energy and they provide no other nutrients to the horse. They have widely different structures and are soluble in either fat or water depending on their structure. Vitamins are classified according to their solubility. The fatsoluble vitamins include vitamins A D E and K and the watersoluble vitamins include the large group of B vitamins and vitamin C ascorbic acid.

The natural forms of most vitamins are present in plant material or the plant material contains the precursors necessary for the horse to manufacture them either metabolically themselves or through a mutually beneficial association with gut microbes.
The fatsoluble vitamins are stored primarily in the liver and for that reason it is possible to feed the horse more than required. On the other hand the watersoluble vitamins of the B group and vitamin C are excreted in the urine or manure if fed in higher quantities than required consequently toxicities of these vitamins are rare.
Fresh pasture is still the best source of vitamins and vitamin precursors for both the fatsoluble and watersoluble vitamin categories. Grains can be a good source of some vitamins as well. Differences in both processing and preserving forages and grains can affect the amount and viability of the vitamins present naturally. Similarly storing forage as hay will result in a rapid decline of natural vitamins in forages. 
All complete feeds available for horses are supplemented with the fatsoluble vitamins A D and E. There is however no requirement under Canadas Feeds Act and Feeds Regulations for horses to include watersoluble vitamins in complete feeds primarily because it has been difficult to prove under research conditions that there is an improvement in equine health if they are added. B vitamins even if they are supplemented cannot be listed on the tag of the feed you buy if the feed is not registered with the Canadian Feed Inspection Agency CFIA but manufacturers of high quality equine feeds often do include