Nutritional minimalists take the position that supplementation of a “quality”[not defined] diet is virtually always a waste of money. I recently read this opinion about supplementing vitamin E: “…Vitamin E deficiencies are occasionally seen in horses that don’t have access to fresh forage, or good quality green hay. But it’s so occasionally that it’s not worth worrying about in most cases, especially if there is green forage or fresh, high-quality hay.”
Green pasture is a good source of vitamin E; hays, not so much.
There are quite a few qualifiers in that statement – occasionally, in most cases, if – and exactly what is meant by “fresh” and “high quality” hay is unclear. Fresh is particularly important here because E is lost as the hay ages. Published levels vary a bit, likely depending on how old the hay was when sampled. Alfalfa is higher than grass hays, with the range for all hay about 30 to 100 IU/kg when cut which drops by 53 to 73% in 12 weeks.
If your horse is mature and basically doing nothing, 10 kg of hay will meet the minimum recommended for maintenance of 1 IU/kg body weight if it is at least 50 IU/kg, so some will do when first cut but within 3 months all hays will be deficient. For growing, pregnant, lactating and exercising horses the current NRC recommended minimum is 2 IU/kg of body weight so a 500 kg horse eating 10 kg of hay may luck out with a hay that was just cut and has the upper level but this won’t last for long. How many horses eat only hays that are 1 or 2 months old?
If you feed a balancer or supplemented grain you are not protected either. Amounts are typically too small to meet requirements and vitamin E, even in protected forms, is not stable for long in a feed or mineral mix. In fact, because of its reactivity as an antioxidant it is commonly used as a natural preservative for the feed.
Inadequate vitamin E intake is associated with a longer list of medical conditions than any other vitamin. These include:
- Neuraxonal dystrophy (genetic predisposition in several breeds)
- Equine degenerative myeloencephalopathy (possibly a more severe form of neuraxonal dystrophy , genetic predisposition in several breeds)
- Pigment retinopathy of the eye
- Vitamin E deficiency myopathy and masseter muscle atrophy
That’s just the more dramatic examples. Vitamin E protects the integrity of every cell with well documented roles in everything from sperm quality to immunity to athletic performance.
Unlike the other fat soluble vitamins, A, D and K, vitamin E is not stored in the liver. Although horses with abundant fat may store some extra, the horse basically depends on a constant dietary supply. This is not a vitamin the horse can manufacture himself or absorb after organisms in the intestinal tract make it.
How to supplement can get a little confusing. In nutrition, vitamin E generally refers to alpha-tocopherol but the term vitamin E covers a family of 4 tocopherols and 4 tocotrienols. Alpha-tocopherol is the form active in the body as an antioxidant. “Natural” on a supplement may mean it contains all forms of vitamin E or may refer to the structure of alpha-tocopherol, the d-alpha or l-alpha form. The d-alpha-tocopherol is the natural, active form, l- being a mirror image which is in many supplements. The recommendation of 1 IU/kg/day for adults at maintenance and 2 IU/kg/day for other ages and classes refers to a mixture of d- and l- forms, d,l-alpha-tocopherol. If using pure d-alpha-tocopherol you can cut the amount in half. Supplements labeled “mixed tocopherols” or “full spectrum vitamin E” contain all eight forms. To know how much to give you would have to know how much of the alpha-tocopherol is in it.
Supplementation isn’t expensive. This is one vitamin where dietary levels and requirements are well worked out. Don’t skip it.
Eleanor Kellon, VMD