If a horse refuses to move forward or rushes backward on the trailer, they’re probably feeling nervous or don't fully understand your commands. The secret to loading a difficult horse is to take it slow and spend ample time on training outside of the trailer. Consider using a training halter to teach the horse to walk forward. Make sure that your horse has developed confidence in you, and that it listens to your commands.  Once you’ve established this, you can try to simulate a trailer-like environment before actually taking the horse to the trailer. Have your horse move forward and step over a pole onto a piece of wood or a mat. Once you’re ready to move to the trailer, practice a few times – and then call it a day. Remember that some horses take a long time to warm up to the loading process, even with professional trainers.