This behavior is actually about teaching a horse to be caught but also gets him familiar with and comfortable wearing a halter.
Goal: Horse nose targets halter, 2 cues (1 is the presence of the harness)
Prerequisite: Targeting level 1, 2 & 3
Since your horse knows how to nose target objects, this should be a snap, unless he has a fear association with the halter already or it has become a poisoned cue.
Start with the halter behind your back and when you have your horse’s attention, present it in front of you and just to one side of his vision and just inside his personal space. Train as for targeting the other objects, clicking for any interest in the halter, looking at it, moving his head or turning towards it, sniffing it, touching it. Reward immediately and place it behind your back between each trial. This keeps it interesting and increases his chances of wanting to examine it out of curiosity. Practice nose targeting it until he is eager to do so. You want this behavior to be strong. Move the halter around on both sides, up and down etc as you did for the object-based training.
The Halter is a Poisoned Cue for him
A poisoned cue is a cue that has a negative association for the horse. He likely associates the halter with the loss of freedom, or even a negative event that has occurred in the past and he wants nothing to do with it! To solve this, choose a different halter than he has never worn before (maybe a rope halter -you can make one of these for temporary use-or one made of a different material or looks very different from the one he is afraid of). Train it as above.
If you MUST use the same halter to train this and if you need to get him accustomed to the old one soon after retraining on a new one), you will need to use a process called ‘counter conditioning’ before starting the targeting. This changes how a horse feels about the halter. In the beginning, you are not going to ask for any physical interaction with it, so don’t plan on catching him to take him anywhere while retraining this. Find another way to handle him or do what you need such as herding him into a smaller pen or using his buddies to call him in).
Choose a reward of very high value as we want to build a positive association with the halter and have them ready with your clicker. Make a big fuss of placing the halter on a fence or on the ground far enough away from your horse so he notices it but also so there is no negative reaction to it (so he doesn’t move away from it, or put his ears back etc).
Any time he looks towards it, click and reward him. After each session, remove it so it will now be a novel object that he gets to interact with only when you are with him.
Each session place the halter a little closer to him, using his body signals as an indicator of how fast to decrease the distance. If he moves away from it, it’s too close. Ideally, he should be able to stand calmly with it nearby. Continue clicking and treating, and decreasing distance each session until he is near enough to it that he can touch it. Now you can start having him interacting with it the way you would if it wasn’t a poisoned cue with one exception: start with it on the fence or wherever it was when you counter conditioned it. When he is comfortable with that, try holding it to your side, then behind you, then in front of you, bringing it out from behind a box or bale of hay etc. This will help to make sure its sudden appearance does not startle him or trigger old memories.
It is VERY important to train at his pace and not to rush him into interaction with the halter. Avoid attempting to put the any halter on him at this point or all will be lost.
Here is a video showing the basic steps in the process with a Donkey. What specific behaviors do you see that tells you the rope is a poisoned cue for this animal?
As you can see, it may not take long to retrain. Remember, a training session might only be 10-15 repetitions of c/t. Then a break for a minute or two and do 10-15 more repetitions. This would be considered two separate training sessions.