Your horse “is” what he eats. Follow these pointers to make sure what you’re feeding him isn’t over-energizing him, especially if he's in a stall and unable to leach out excess energy.
Balance the in/out. Like you, your horse maintains his body weight and energy levels by taking in the right amount of feed based on his daily work (exercise). Many nervous, spooky horses are simply getting too many calories for the amount of riding they’re given. (For an illustrated body condition scoring chart, search the phrase at HorseandRider.com.)
Watch the high-energy carbs. Nature didn’t make horses to eat grain, and the simple carbohydrates and starch found in cereal grains such as corn, oats, and barley can be especially problematic. Favor instead complex carbs (e.g., hay, beet pulp) and fats (e.g., soybean oil, rice bran). (For more on feeds, review January’s Horsekeeping page, “What’s in Your Horse’s Feed?,” at HorseandRider.com this month.)
Consider a supplement. If you feed and exercise your horse correctly and he still seems amped up, ask your vet about the advisability of a calming supplement. Depending on your horse’s unique needs, ingredients such as B vitamins, (especially B1 or thiamine), tryptophan, magnesium, valerian (an herbal related to valium), or the hormone progesterone may help.