This works best if he already loads easily.
Have the horse face the trailer, ask him to put one foot in, don't let him go any farther than that, just one foot. Then have him take it out. Do this several times, 10 or 20Xs. Next step ask for both front feet, no farther. Then ask him to take both feet out of the trailer, do that several times, 20 or 30Xs.
Next step if you can get three feet in great, but sometimes that can be difficult so four is fine. Then ask him to get out of the trailer after a second or two. He should remember the step is there and since he has gone up and down 50 or so times by now. He should not be frightened and get out easily, if he doesn't get out easily, start again from the beginning. If he does get out easily, repeat all the way in and all the way out several times.
My clyde wouldn't get out of the trailer and when he finally came out he would fly out and the last thing throw his head up and hit the top of the trailer, even though I had an 8' tall trailer this was scary to watch. I hired a John Lyons certified trainer to help me, and the above discription is what he did. It worked great. If I didn't trailer him any where for awhile I would give him a short refresher course.
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