If you could I would practice a few times before hand or make sure you have the time to work through the problems. I generally keep a hay bag in the trailer which most of the horses learn to be content standing in there when they have something to munch on. First off just calmly with an "I've got all day" attitude look forward and try walking him up into the trailer. If he goes up there then give him lots of praise and make sure you get the door closed before you tie him. (If a horse backs out while tied they will either struggle and get hurt or break the tie which isn't very good either. I've had this experience and definitely try to avoid it. Quick release does no good if your horse is flopping around and you can't safely get to it.)
If he does not go up then don't sweat it. I will tell you now just don't get frustrated and make sure to stick to your guns. It can be very easy to get flustered if people are watching or pressuring you so if you can ask them to chill in the truck or something it could help. If you just really would like to get it done and over with you can try just once to entice the horse with grain, especially if it is very much a pushover when it comes to food. But make sure to time it right, or just leave the bucket far enough in the trailer so the horse can't eat it while having its front legs in and no backs.
If that doesn't work I'd take a more natural horsemanship type approach which could take a bit depending on how quickly your horse catches on. What you do is stand by the back of the trailer with lead rope in your left hand and whip or carrot stick in your right. Make a defined pointing motion inside of the trailer and give the horse a few seconds to react. After that introduce rhythmic tapping right behind the withers while still pointing. If the horse backs up or doesn't move you can increase the intensity of the taps. The very moment that horse moves forward gently drop all body language and let the horse chill. If the horse has an interest in the trailer let him sniff for a few moments than ask for more. If he is flustered and looking around get him paying attention to you.
When you ask him to move forward again begin by picking up your body language and pointing into the trailer, introduce tapping until he moves forward. If he backs up and shuts you out try to get behind his shoulder and move with him. Even if you end up miles away from the trailer still reward forward motion. But when you are following him keep your hand pointed and keep tapping. You could also go on Youtube and look around at videos of people trailer loading using a natural horsemanship approach.
I can vouch to say that if you do it right it will work. But if you ever get worked up and upset with your horse then they've one. Stick to your guns and reward every time your horse gives you a little bit.
One of my mares, Scarlet, is so big that you can't out muscle her and get her into the trailer. There really is no cheating with her. One time we actually got her loaded to go to the trainer's and she was tied before closing the door and she felt a little pull and set back. She pulled hard enough where she broke the tie! We could not stay calm enough to get her to load and just ended up taking a different horse. After that the trainer showed us with our other horses how we should load her and we did. Now we just point in the trailer and she'll step right up there with no problem. Most of the problem was other people yelling at me and trying to rush me. It took a some time and a lot of understanding but it was well worth it. Now I can load her and my gelding at the same time no problem. Some of my other family members have difficulties even when they are good with me because they cannot keep themselves calm.
Sorry about the novel but I figured I'd explain in detail. x) Good luck with your horse, now that I've seen how easy it can be I just would love everyone to see it as well.
Last edited by ButtInTheDirt; 06-14-2012 at 12:29 AM.