Why Your Horse Needs Vitamin E

An equine diet based solely on hay may be lacking in this essential nutrient.

Hay is almost the perfect food for horses—most varieties offer the right balance of protein, fiber, nutrients and energy to keep the average horse healthy.

The key word there is “almost.” One nutrient that hay may not provide in sufficient quantity is vitamin E. This essential nutrient is present in fresh pasture but begins to degrade as soon as grass and legume plants are harvested. And the longer the hay is stored before it is consumed, the more of its vitamin E is lost.

So for horses whose forage comes primarily from hay, with little or no grazing, vitamin E deficiency is a possibility. And it’s even more likely for horses who are in training with limited turnout because exertion increases the need for this valuable antioxidant. Vitamin E requirements are also higher for aging horses, those who are ill and those with certain health issues.

Vitamin E helps keep a horse’s muscles, nerves and all his internal workings functioning smoothly. And if he’s not getting it naturally in a green pasture, then you’ll need to find a way to add it to his diet. Here’s a look at what vitamin E does and what you can do to make sure your horse gets enough—but not too much.

Vitamin E in nature

“Vitamin E” is a collective name for a group of eight naturally occurring compounds that all have distinctive antioxidant activity. There are four tocopherols and four tocotrienols. Each is designated with an alpha-, beta-, gamma- or delta-.

“The most biologically available form is alpha- tocopherol, and this is why we can measure this one in the blood,” says Tania Cubitt, PhD, an equine nutritionist with Performance Horse Nutrition, a consulting firm in Middleburg, Virginia.

If a horse has access to fresh pasture, he will get plenty of vitamin E in his diet.

Vitamin E is fat-soluble, which means it’s handled quite differently by the body compared to water-soluble vitamins, such as vitamin C, which are not stored and are eliminated in urine if too much is consumed. Fat-soluble vitamins can be stored in the liver and the body’s fatty tissues. This means the horse can keep a supply of the nutrient when it is abundant, and access it when it isn’t. And that’s exactly what he does in nature. Vitamin E is abundant in fresh, green grass, but the amounts diminish as grass matures and dies. Horses who spend the winter foraging on dried grasses will draw on their stored vitamin E; then they will replenish their supplies of the nutrient when the green plants start growing in the spring.

All of which means that a domesticated horse’s lifestyle can work against his receiving enough vitamin E. “The normal horse under natural conditions is able to cope with seasonal fluctuations,” says Cubitt. “We have thwarted this, however, by putting our horses in an artificial environment. About 30 to 80 percent of the vitamin E in hay can be dissipated during the drying for harvest and during storage. If horses are stuck in a stall and not on pasture, they are relying on us to supply most of their vitamin E. I have seen a lot of horses that are actually deficient in vitamin E because of the way they are managed. So today we see a lot of horses being supplemented with vitamin E.”

What Vitamin E does for horses 

Vitamin E plays a role in many functions throughout the body, but it is known primarily as a potent antioxidant, meaning it binds with and limits the damage caused by free radicals, which are atoms or molecules with an odd number of electrons. Because they have an unstable electrical charge, free radicals tend to “steal” electrons from other molecules to become stable. But when the original molecule loses its electron, it becomes unstable and in turn tries to steal another electron from somewhere else.