Sounds like he was stepped on.
My first mare had her back hoof split In half before we purchased her because she was stepped on in a slant load trailer. If the force was so hard to break her hoof, wraps wouldn't have helped too much. The dividers didn't go all the way to the floor. Luckily,she's now 25 and hasn't had an issue with it ever.
If they are In a straight or slant load with dividers, I use polos or sport boots with bell boots until they are used to it.
In a stock type trailer I just turn them loose and don't wrap unless quarters are tight.
For minis, and only minis, not ponies, if they are loose on a stock trailer I would not bother. They aren't heavy enough to cause real damage. They aren't shod either.
I always tie in straight or slant loads. Stops them from turning around and getting stuck. In a stock trailer I just turn them loose. Easier to balance.
My filly was in a very very bad trailer accident. She got her front feet over the chest bar, I was in the process of freeing her when my mother jumped up into the escape door and screamed whoa in her face (yes, I still want to kill her for it, she's had horses a long time). He back feet slipped and she got her breakaway halter caught on a ring used to hang the hay bag from. She was choking herself. I had to cut her halter off. She then flopped onto her back cast against the ramp of the trailer.
We had no extra halter. I Climbed in with her, put a dog leash on her face, then held her down as the door opened.
She stayed down until we had dividers moved. Then she hopped up and I turned her around and got her back on the trailer. She hasn't been a stupid head in the trailer since.
She wasn't wrapped and she was in a breakaway. The breakaway didn't break. It was ancient and crappy too, the pressure just wasn't In the right spot. She has a small scratch on her hind pastern which she thought was life threatening and super painful, but it was gone in 2 days (as was her three legged limping) and there is no scar. No doctoring either!
The breakaway didn't save her, me being good with horses and having a knife saved her. If I hadnt of had my knife my filly would have died in front of me. We now mount one with a cow magnet in the trailer. If I hadn't had a bond where she trusted me to lay on a ramp with traffic flying past her while injured, she, I and likely an ***** motorist would have been hurt or worse.
In my opinion, The best thing you can do to protect the safety of your horses while trailering is to be competent and use common sense. Keep your trailer maintained. Have your horse trained. And if you're hauling a wild one, be good enough to handle it and be able to think through potential situations.
