How do I stop my horse from backing out of the trailer before I am ready?

A horse that immediately backs out of the trailer as soon as it has loaded has not learned to stand quietly inside and wait for the handler's cue to exit — it is self-releasing from the exercise rather than waiting for permission. This is a manners and patience problem, and it is best addressed by teaching the horse that backing out is only allowed when the handler asks for it. Begin by rewarding the horse heavily for standing inside: feed small pieces of hay, let it eat from a hay net, stand quietly with it, scratch its withers. The horse should begin to find the inside of the trailer a pleasant place to stand rather than a place to escape. When the horse does attempt to back out without being asked, block the exit with your body positioned safely to one side — never directly behind the horse — and apply rhythmic forward pressure with the lead rope or a tap on the hindquarters to ask it forward again. Do not become a pushing contest at the door; instead step aside if the horse is committed to coming out, let it exit, and immediately ask it to reload. The act of backing out earns the horse more work, not a rest. Over repetitions the horse learns that standing quietly inside is the path of least resistance. Closing the trailer door promptly once the horse is calm and fully loaded prevents the backing temptation, but the horse should also learn to stand with the door open before you rely on the door as management.