Teach a horse to back on hand on the ground first, then on uneven ground, then between something or other, then around the trailer.
Last in the trailer, once he knows well what backing is.
I used this with my mare who did not back out of a trailer. I backed her up and down a small slope in front of the barn. Also backed her into her stall, which has about a 4" drop. And I backed her a few other places that I can’t remember. After all that she now backs out of a trailer with no problems.
It’s never a bad idea to teach them to back in hand. But…My horse is perfectly obedient about backing in hand, doing ground work, etc., But he still didn’t want to back out of that straight load ramp trailer. ðŸ˜
They have to be taught in increments. Start with 2 hooves on and back off.
He’d never been in a straight-load, ramp trailer. Always rode in my step-in slant without a divider. I hadn’t anticipated there would be an issue He loaded fine. After the fact, I’ve given him load/unload lessons in a straight-load.
The same happened to us. A palomino dumped on us. We were going to Friday Night Jumping. We put him on early just to see if he would load. Yes he did but wouldn’t unload. He wanted to turn around but was now too big. So we left him in there and fed him in there. Loaded the other horse later and went to the event. They both unloaded fine. We then did the incremental training and he was fine