I have a 3 year old gelding that has taken his headstall with no problems until just recently. He takes the bit just fine but when you go to put the headstall on he resists by throwing up his head. This started about a month ago after we trailered him and he fell in the trailer. He was tied up and fell, we stopped the truck and by the time we got out to help him he had regained his footing and got up. He did not have his headstall on just his halter.
He doesn't have a problem putting on his halter just the headstall.
Any suggestions on how we can get him to let us put the headstall on again and why now all of a sudden he won't take it?
I would guess that your gelding is now sensitive around his ears due to injury during his fall in the trailer. Since the halter is fastened behind his ears that would be the reason that he does not mind having it applied, however, the headstall must be put on over the ears and this is why it must be bothering him.
I would begin by desensitizing him quietly around his head. Be gentle and easy with him, remember that he is not being disobedient, he's just afraid. Put on his halter and rub your hand softly over his muzzle, working your way over his cheeks and forehead. When he will accept this, rub your hand over his forehead and ears, about 1/2 way down his neck. Do not make an issue out of touching his ears, just gently keep petting and rubbing his face, over the ears and down his neck.
I would also work on teaching him to drop his head by applying downward pressure on his lead rope. Stand on his left side at his shoulder with your hand just below the snap on your lead. (I recommend using a rope halter for this lesson as horses learn from release and this form of halter gives quicker release for faster learning.) Gently apply downward pressure on the rope until he drops his head, the moment that he puts it down, even a tiny bit, RELEASE. If he throws his head up the first few times, just maintain the pressure until it comes down a bit. Remember to reward him with releasing the pressure as soon as he puts his head down a bit, and before long you will be able to drop his head all the way to the ground. When he's handy with this exercise, try getting him to drop his head by putting your hand on his poll (the area right behind his ears) and applying slight pressure.
Repeat these exercises for a couple of days in a row, and make sure your horse is learning not to be afraid of having his ears handled before trying to apply the headstall again. I believe that with time and patience your horse will once again be easy to bridle.
Thank You and Happy Trails!