As already mentioned, I would make sure there is not any issues with your trailer (unsteady; electrical shocks; bees; etc) and any issues with the horse (sore feet; hind end lameness; etc).
But most of the time … the horse simply just decided she didn’t want to listen to you.
You don’t have a trailer loading problem - you have a manners/respect problem (or whatever you want to call it). You have a training problem.
While the trailer itself is actually irrelevant, you need to TRAIN your horse to load. Control the feet. If you have true control of the feet, you can direct your horse anywhere. Chances are, there are other situations where your horse has decided not to listen to you. This trailer loading problem is just another one of those.
I primarily rodeo and my horses and I travel every single weekend, and sometimes in friend’s trailers. They self-load and self-unload upon command. If you go through the appropriate training, trailer loading is a non-issue. (along with many other things…) Of course, it took me some time to learn this myself, but haven’t had an issue in years.
I wrote this up on another board. It’s worth a read.
Prepare your horse.
You need to prepare your horse before you actually introduce the trailer. Ground work is key! Your horse should lead respectably beside you (not in front of you, and not behind you). Your horse should always respect your space and never crowd you. Your horse should move his hindquarters away from you (disengage) when you tap his hip and ask him to move over. He should also move his shoulders away from you when you tap his shoulders. And he should back up freely when you ask.
Teaching your horse proper ground manners will take weeks, or even months. This is not something that can be learned in one session. And it is something that you must always expect your horse do. Don’t ever “slack off” and let your horse get away with bad ground manners. Always expect perfection. And if the horse screws up, that’s okay! Correct them, and go on with what you are doing. Horses are like humans in that they will make mistakes. But that’s okay because that’s how the horse learns.
The best way to teach ground manners is to work specifically on it every single day for 10 to 15 minutes.
Also remember, when teaching your horse ground manners, you don’t need a death grip on the halter or lead. In fact, go ahead and give the horse a foot or two slack in the lead rope. This teaches the horse that they still have to behave and listen to you, even if you aren’t directly beside them. Ideally in the end, you should be able to move every part of your horse’s body (head, shoulders, hip, and all four feet) without your feet ever moving one step. THAT’S control. And that’s the level of ground manners you need from your horse before you can ever expect them to respect and trust you to load into a trailer.
I find it very useful to use a stick (about 4 feet in length) to act as an extension of your arm to move various body parts of the horse. However, as an end result, you should be able to move your horse’s body with your body language.
Key point: Your horse must respect you and trust you with excellent ground manners before you even introduce the trailer.
Introduce the trailer.
One mistake that most people make when introducing their horse to the trailer is that they must get the horse onto the trailer during one session. That is incorrect. The very last thing you should do is expect your horse to fully load. And I’ll explain more on that below.
When you introduce the trailer, it is simply going to be a mere obstacle for you to work around. Make sure your trailer is parked in an area with good footing and plenty of room. If you have a smaller bumper pull trailer, it is safest to have it hooked up to a pickup, or else appropriately blocked. You wouldn’t want the trailer to move if you horse puts weight in it. Larger gooseneck trailers are often heavy enough that it isn’t necessary to have a pickup hooked to it, but you should still block the wheels for safety reasons.
For the first couple of sessions, open up the trailer and just work your horse near it. Continue doing the same ground work exercises you did before. For example: You stand at the trailer opening. With a lunge line and “stick” ask your horse to move its body to the right in a half-circle. Then ask your horse to go the left. Change directions again. Etc. Basically, you are keeping your horse’s feet moving by asking the horse to move in various directions. Remember: The horse should be moving; not you! (If you did your ground work correctly.)
If you horse ever wants to stop and sniff/smell or otherwise investigate the trailer, allow them. It is okay for them to show curiosity toward the trailer, because that means they have their attention on it.
So for your first couple sessions (remember: we are working with our horse every day for 10 to 15 minutes), you are not even asking your horse to put one foot on the trailer. This is what most people don’t understand, because they think they have to get that horse in the trailer, which is incorrect.
Begin teaching the loading process.
Now that your horse has great ground manners, and can still uphold those ground manners when the trailer is present, you are ready to start teaching the horse how to load and unload from the trailer.
Some people will tell you to lure your horse onto the trailer with grain. That’s fine and dandy, but what will you do when your horse is not interested in treats? Giving your horse treats does not actually train the horse to load onto the trailer. It can be used as a reward/praise, but it should never be used to trick a horse into loading.
Some people will also tell you to park your trailer in the horse’s pen and put your horse’s food and water in the trailer. The idea here is that the horse will become so hungry and thirsty that they will get into the trailer to nourish themselves. This is not only animal cruelty, but it also does not train your horse to load because the handler isn’t even there! And there are some horses out there that would rather starve themselves instead of setting foot into the trailer.
So, we want to teach the horse to load when we ask it to. Not only when there is food present. And please note it does not matter what type of trailer you have (stock, 2-horse straight, ramp, etc). Yes, a wide open stock trailer will be easier to train, but you can train a horse to load into anything with patience.
We start the trailer loading process by asking the horse to load ONE front foot ONLY. Standing off to your horse’s left side, tap your horse’s hip to encourage him to go forward. Do not stop asking the horse to go forward until he does. But when he does comply, you must immediately stop asking him. You don’t need to coddle the horse every time he does something right, but you do need to remove the pressure (you tapping his hip to go forward) for the horse to get his release and reward. If your horse steps sideways instead of forward, that’s okay. Use your previous ground manners training to straighten him up again. He must face the trailer opening squarely in order to load, so you must keep his body square to it.
Again, if he sniffs or investigates the trailer, allow him to do so because he is showing interest in it.
Be patient. Keep on asking your horse to go forward until he places one foot into the trailer. Once he does so, allow him to keep it there and think about it. But you need to be aware of his body language. If you sense that he is about to take that foot off the trailer again, you need to beat him to the punch and ASK him to back up before he actually does it. That way, he thinks it was your idea to back up; not his. Then repeat! Ask him to load only one front foot and then unload it.
Remember to always end your daily sessions on a positive note. And remember that horses have bad days too. Maybe yesterday he loaded one foot just fine, and now today you are having issues. Instead of drilling him for 45 minutes to get that one foot on the trailer, go back to just plain working on ground manners because it is something that he can do correctly. End on a positive note, quit, and try to load one foot the next day.
After several sessions (and several days) of loading just the front foot when you horse is consistent, then you can start asking to load both front feet. Go through the same process you did before of asking your horse to move forward by tapping him on the hip, and releasing immediately when he moves forward correctly. Then asking him to back those feet off. This is an “approach – retreat” sort of method. You are telling the horse “Hey, I would like you to come forward.” and once he does you tell him “Oh wait, I changed my mind. I want you to back up.” By asking your horse to go forward and backward in a non-chalant manner, you are teaching him that trailer loading is no big deal and he is able to listen to you on where you want his feet to go.
On a side note, you as the handler have never yet set one foot into the trailer. Why? By staying outside of the trailer, you are slowly teaching your horse to self-load. Especially for slant load trailers, this is much safer staying outside of the trailer, and only entering the trailer to close the divider behind the horse.
After several session (and several days) of loading both the front feet, you can begin to ask the horse to load three feet. Do NOT allow your horse to load fully. He is not ready for that. Ask him to load and unload three feet over and over again in your daily sessions, using the approach-retreat method.
Key point: It should have taken you a couple weeks to get your horse to the point of loading three feet in and out of the trailer. This is not a process to be rushed. You must stay patient.
The final step: Loading your horse into the trailer.
When your horse is successfully loading three feet in and out of the trailer easily on command, you are finally ready to ask the horse to load fully. Use the exact same process you were doing before. You are just simply going to ask for all four feet to be in the trailer at the same time. And then you are going to ask the horse to back off the trailer.
This is why we’ve spent weeks (or even months) of preparation for this moment. We’ve perfected our horse’s ground manners. We’ve introduced the trailer as a non-scary object. We’ve got excellent control of all four feet and the horse’s whole body. This is what is needed to have a horse who loads into any trailer without question.
Just as we’ve done everything else in baby steps, you will NOT load your horse completely for the first time, slam the divider shut, and take off down the road. You will instead load and unload your horse several times over the period of several sessions. When your horse is comfortable with that, then you can close the divider (if your trailer has one) for a few minutes. Do that for a few sessions. When your horse is comfortable with that, you can completely close the trailer for a few sessions. When you horse is okay with that, then you can take them for an easy drive around the block for a few minutes. Often, this step is much more calm if you haul your horse with a buddy who travels well.
Conclusion
As you can see, to properly teach your horse to load (or to fix any bad habits) this is a long process over the course of weeks or months. It requires patience and it requires your horse to respect and trust you.
And remember: There is no shame in seeking the help of a trainer if you have a hard-to-load horse, no matter how old you are or how long you’ve owned horses. Everyone can always learn something from someone else.
I personally highly recommend Clinton Anderson’s trailer loading DVD. It goes through most everything I just talked about, and along with more details and video to see what is going on. I’ve had great success with this method with my horses.