Why does my horse back out of the trailer as soon as it loads, and how do I fix it?

Premature backing is almost always a combination of anxiety about being enclosed and the absence of a trained cue for when exiting is appropriate. The horse that has never been taught to wait for permission to exit will always self-release when its anxiety rises, because backing out has never produced a consequence that discouraged it. Address the anxiety first: spend time inside the trailer with the horse doing nothing other than standing, feeding, and relaxing. A horse that is genuinely comfortable inside the trailer does not feel the urgency to leave. Tie the horse at a length that allows it to stand comfortably with its head in a natural position but not so long that it can swing around — many horses back out partly because they have turned sideways and are no longer aligned with the exit. Teach backing on cue from the ground so the horse understands that backing is a specific requested behavior, not something it initiates on its own. When the horse backs without being asked, immediately redirect it forward and reload without drama or punishment. The pattern — back out uninvited, reload immediately, try again — repeated consistently teaches the horse that self-releasing does not result in freedom. Progress to closing the divider or door once the horse stands reliably with it open, always building the duration of quiet standing before adding the confinement of a closed trailer.