Vitamin E is an essential nutrient in the equine diet, meaning horses cannot make it themselves and must consume it through their diets. Horses can easily meet this requirement with adequate access to high-quality pasture. However, vitamin E levels drop rapidly in preserved forages (think hay). And horses with decreased vitamin E levels can be at risk for developing some neuromuscular conditions. As such, owners might need to supplement this vitamin in their horses’ diets, one veterinarian and researcher said.