I watched the donkey video. I would not try snubbing a horse to a trailer like they snubbed the donkey in this video. Even a horse that is broke to tie solidly will set back. Unlike the donkey (that sulls), horses sull and then take huge 'blind' leaps forward.
If you do this with a horse that does not want to load, it will usually cut its head half off or paw out and cut its legs to the bone. I cannot count how many horses I have had to teach to trailer load for other people and they had the wounds or scars from owners trying to snub their horses to a trailer to get them in.
We use a flat web halter and run a 1/4 inch nylon cord under the horse's chin or under its upper lip and teach it to go forward. The string draws tight and is uncomfortable if the horse does not lead forward. The uncomfortable pressure of the string will release when he comes forward. You can load any horse in a trailer in a few minutes once you learn the correct timing of the release.
Don't try the trailer at first. Take a few minutes to teach the horse to come forward for the release at other obstacles. I lead them over a piece of plywood, take them up onto a cement slab, lead them over some big poles on the ground. I find something they do not want to lead on or over. If you pull lightly and steady, the horse will eventually take a step forward. When he does, put slack instantly into the lead. Horses very quickly learn to step forward to get that release.
Then, most just step right up into a trailer when they are asked with that light pull on the string.
It is very important that you do NOT pull hard and do NOT jerk the lead attached to the string. This will get a horse 'reactive' and get him 'on the fight'. A reactive horse is not going to load anywhere for you. You only want it to be uncomfortable and do not want it to hurt. If you start hurting the horse with the string, he will either fight you or tune you out (sull) and it is all over until he settles back down and starts thinking again.
I have used this technique on horses that have refused to load for more than 10 years. Many had scars from the failed attempts. Owners could not believe their eyes.
You can load a horse a few times like this, always using a 'smooch' to ask them to move. Then, you can just lead them to the back of any trailer, smooch and they step right in without even leading them in. I have been doing this for about 50 years and it has not failed yet.