I'm interested to know how you drive with him in the trailer. Often a horse will start refusing to load when it feels wary and out of balance in the trailer. If you have taken a corner to quickly or hit the breaks, it's totally understandable that the horse would refuse loading after a bad experience.
Another possible reason is that he has 'pulled the wool over your eyes'. Maybe you're not as straight down the line 'these are the rules' as his old owner, and he's worked that out. Horses are very quick to pick people who they can walk all over.
If he hasn't had a bad experience, then I would not be mollycoddling him top get into the trailer by feeding him and acclimatising him to it. Obviously if the horse used to load with no problems previously, he is just trying you out and you really need to establish who is top dog before even thinking about trailering.
Do a lot of ground work, asking him to back up, yield his hind quarters and shoulders in both directions, walk forward when you ask, halt when you ask without moving into you, and dropping his head from light pressure on the halter.
Invest in a firm dressage whip, and teach him o move away from it. Not by belting the bejesus out of him, but by tapping him lightly but persistently on the hind quarters with it. Horses learn not by pressure itself, but through the RELEASE of pressure. So the tapping whip is an irritation, he is uncomfortable standing there being tapped, so will take a step forward. This is the response you want, the second he steps forward, stop tapping. Ask him to walk on again just with a light pressure on the halter. If he doesn't walk, go back to tapping. If he backs into the tapping, tap harder and faster until he steps forward, even just one step is enough to have the pressure released.
The tapping method just gives you back up in case he decides to get strong again when you introduce the trailer. There is absolutely no point at all in pulling on his head trying to drag him into the trailer, a horse will simply lean against this type of pressure on the head and you can do a lot of damage to his poll.
When he'll walk away from the whip every time (and you should be able to just show him the whip and he'll move away), introduce the trailer.
Open the centre divider up so the bay is nice and wide for him to go into, and open the front door to lighten the trailer up, making it look more inviting.
Stand by his shoulder, whip in one hand, and confidently ask him to walk on with the halter. If he stops, ask once more, and then start your tapping until he walks forward again.
This can take a while, but has worked on every horse I have used it on, from stubborn kids ponies to flighty ottbs and 'slow' wb's. Basically the theory is, make the outside of the trailer uncomfortable, where he gets tapped, and the inside comfortable, where he does not get tapped.
A few points to note:
- Practice this daily or twice daily for short bursts. Until he is walking confidently onto the float and standing in there with no encouragement, and allowing you to slowly back him out again, absolutely DO NOT! Close the back on him. You can't rush these things!
- Make sure that he will stand quietly in the float on his own. If he goes to back out, tap him. Make the outside uncomfortable, and inside comfortable. Until he will stand quietly for as long as you want him to. A horse should not have to be trapped in the float by the breech gates/doors - this is very dangerous as the horse can't go anywhere while travelling, but when you go to unload them, there's a very good chance that the horse will fly out at a million miles an hour, taking out anyone standing in his way!
- When he's happily loading, standing and unloading, THEN you can start closing the back on him. DO NOT tie his head in before you close the back. My father float trained a horse for a friend using the tap method, this horse had had some very bad experiences floating and it took a week of daily work to get him confident. We then left it to the owners, who proceeded to load him, tie his head to a solid metal chain in the float BEFORE doing the back up. Of course the horse freaked out, went to run backwards and couldn't, so flipped upside down and almost broke his neck. He had to be dragged out of the float on his back.
Don't tie a horse before you close the back.
- When you can close the back and the horse will happily stand, try taking him for a drive around the block, taking it very easily. You don't want to hit the breaks and scare him on his first trip out.
Take him straight home and unload him, put him back on, make him stand, then unload again and put him away.
- Try taking him a short distance from home (walking distance just in case!), unload him, walk him around and re-load then take him home.
- And one last thing, my pet hate. Please don't 'bribe' him in with food. This is just plain stupid. The horse will run in, grab a mouthful and run back out.And if you DO manage to get him loading and are quick enough to lock him in before he runs out... that's great until you go to a show and realise you don't have any food left for him to get him home again. Good luck with that! It teaches him nothing. Once the horse is floating confidently without food, THEN you can put a hay bag in there if you really feel the need to. But not before he is already loading with no problems.
Now you're right to go ;)