Do you supply horse tack or horse feed to an equine athlete in North Carolina? For feed, Hay or grass can be fed right up to the time of competition. Grain or feed concentrates that are high in starch should be fed at least 4 hours before exercise or competition. The sugars and starches in grain will produce a rapid rise in glucose in the horse’s body. Insulin will then rise to compensate, interfering with proper glucose metabolism.