Vitamin E Deficiency in Horses
Updated: May 11
My good friend Shelly recently started a study on Vitamin E deficiency in horses, concentrating mainly on Iberian & warmblood breeds, but also taking all breeds into account. She initiated the research because one of her beautiful PRE stallions, Petrone, was having a tough time building muscle. His topline was sinking as if he was aging rapidly. His hip bones stuck out, yet he was not underweight. He also had some minor undiagnosed hind end lameness issues. One thing about Shelly, she will do anything and everything for her animals. After over a year of trial and error, and doing every test trying to figure out what was going on with Petrone (with no clear answers), one of the various blood work tests came back with him having low vitamin E levels. I am glad to report that Petrone is being supplemented with Vitamin E and is now doing better than ever.
After this experience, Shelly decided to test all of her horses. Some came back normal, but many of them came back with low vitamin E levels. She opened a research forum on Facebook where she is gathering data on Vitamin E levels in horses all over the country, with a focus on Iberian breeds. As a forum member, I was astonished at the number of horses (all over the country) testing low for Vitamin E.
What is Vitamin E, and why is it so crucial in horses?
Vitamin E is a vital part of horse nutrition. Horses can't produce vitamin E; therefore, it must be provided in their diet. Vitamin E does require a small amount of fat to be adequately absorbed.
Vitamin E has multiple vital roles in the equine body, including; immune response, nerve and muscle function, and antioxidant actions. Vitamin E supports healthy muscle function, helps to prevent muscle disease, and provides antioxidant protection for body tissue, membranes, and enzymes.
Vitamin E itself is a term used to describe a group of compounds known as tocopherols and tocotrienols. With equines, we pay the most attention to alpha-tocopherol because it plays an essential role in protecting cells from oxidative damage. By deploying antioxidants in the equine body, vitamin E helps the body control free radical damage. To avoid oxidative stress or injury, the number of available antioxidants in the tissues should outnumber the free radicals.
As exercise increases, the demand for muscle energy increases, but so does the number of free radicals being produced. Adequate levels of antioxidants should be available to help counter the free radicals and help avoid damage to muscles during exercise. When a horse's workload increases, so do the vitamin E requirements. Signs of oxidative damage in working horses include muscle soreness, stiffness, lack of muscle, weak topline, and slower-than-expected recovery from exercise.
The National Research Council (NRC) equine requirement for vitamin E for a mature 1,100lb horse at rest* is 500 IU per day. Once a horse is in light work, this requirement increases to 800IU. Heavy work requires a minimum of 1,000 IU. However, many researchers feel the NRC underestimates vitamin E requirements, especially in working horses. Currently, the upper suggested limit for vitamin E is 10,000 IU per day. This amount is often given to horses with neurological diseases such as EPM, wobbler syndrome, viral infections, and degenerative conditions such as EDM. EDM or Equine Degenerative Myeloencephalopathy is also linked to vitamin E deficiency in young horses.
So why are so many horses testing low for Vitamin E?
The primary source of vitamin E in horses is fresh green forage. Generally, horses consuming 12 hours or more of fresh grass are not deficient in Vitamin E. However, many horses don't have a housing lifestyle that allows 12 or more hours of access to fresh pasture. Vitamin E rapidly disappears during hay harvesting, with 30-85% lost initially and further loss continuing during storage. Because of the large number of horses that mainly have hay as a forage diet, manufacturers routinely add Vitamin E to commercial feed mixes. However, commercial feed companies are not obligated to state the form of vitamin E in their feeds.
The form of Vitamin E in the diet is also essential. Natural d-alpha-tocopherol is absorbed more efficiently than synthetic alternatives. Additionally, each horse absorbs vitamin E differently. That's why it's important to provide at least the minimum NSC required vitamin E levels and to test each horse individually and see whether further supplementation is needed.
Vegetable oils are relatively high in vitamin E but generally are not fed in elevated enough quantities to supply enough vitamin E to a horse's diet.
Supplementing vitamin E is best achieved through a natural, water-soluble product like Kentucky Equine Research (KER) Nano-E®, which uses liposome encapsulation to deliver the highest level of bioavailability to the horse.
*PRE & Lusitano Owner Forum – Home of the Vitamin E Study - https://www.facebook.com/groups/PRELusitano/