Join Date: Feb 2012
Location: Bellingham, Washington
What kind of a trailer is it? Straight or slant? I personally do not like straight loads and work with slant loads, but here is what I do with my horses who don't trailer well.
How close can you get your mare to the trailer? Walk her towards it and when she starts getting too tense, stop her there. If she's staring at the trailer, let her stare at it. Take your grooming bucket with you and start brushing her. Every time she looks away or puts her head down, or stops concentrating on the trailer, move her closer to it until she's looking at it again. When she puts her attention to something else, it means she has accepted the trailer is not a danger at that distance, so make the distance shorter.
Repeat that process until you get her to the trailer. This process might take several days or even weeks, let her go at her own pace. Do it every day you see her. Once she comfortably walks to the trailer without needing to stop, tie her to the trailer and groom her for the first time. The second time tie her, groom her, and then put up a hay bag for her and leave her there for half an hour or so. If she freaks out, go to her, untie her, calm her down, groom her there and quit. Try again the next day. When she's comfortable with the trailer and eating there start banging around the trailer so that the noises it makes won't scare her. Open the back until she's comfortable watching the door swing. Make sure you have a quick release knot in case she freaks out.
My next step is to tie and groom on the side of the trailer as the horse is comfortable with already, and open the trailer door. I put a grain bucket just inside the trailer on the floor. Make your horse aware you have a grain bucket and where you're putting it. Untie her and allow her to come around the corner to look inside the trailer as she eats her grain. When she is comfortable with looking in the trailer and eating grain at the end, while she is eating, walk in and play with the partitions. You might need a friend to hold her in case she runs, or have them open the partitions for you.
Then start graining in the middle of the trailer, far enough that the horse has to talk in to get it. Once they are comfortable walking into the trailer, put a hay bag up where you plan to tie her. Walk her into the trailer and let her eat there without tying her until the second or third time you do this. If she is comfortable enough, tie her there and leave her alone while she eats. Once she gets comfortable being there slowly introduce the partition, closing it until she is too uncomfortable and then backing off. Eventually you will be able to close it on her, and then leave her there to eat. Your horse will safely and comfortably be in the trailer!
I always hay my horses while I trailer anyway, so they associate trailering with comfort and food. If possible, also teach your horse to trailer even better by driving just down the road for 5 minutes at a time first and then start going for longer. It is hard work to keep their balance in there, so it's best to trailer them for short distances first and often so they learn. Eventually they will be comfortable in a trailer, moving or not. The process of desensitizing them to the trailer takes me a month or so on the worst cases, and then I spend a month trailering them at least once a week if not twice to get them used to the motions. After that I trailer at least once a month.