He STILL has issues with letting me pick up that hoof. 
My mare hates her back hooves being picked up because before I got her she got her leg stuck in barbed wire and really cut it up. So it is sore sometimes. It still is scabbed over.I bet the trainer person tied a rope around their back legs. Smoke had a scar almost exactly like that when we first got him. He would fight with their stud (GO FIGURE), so they tied his back feet in an attempt to stop it.
My initial thought was barbed wire or from standing in mud, she's had a small crack before on one of her legs when the weather has been bad, it healed completely and this one looks much worse
Very possible that she could have got tangled in something. What if it was a cut from barbed wire and standing in the mud mad it worse/crack? Is that possible?
I'm looking at this image in particular. I see a single line running almost diagonally across the back of the pastern. Though a fungal infection of the skin (like scratches) can appear somewhat linear, in this case, the rest of the skin on the heel, etc, looks perfectly clean, with only this single narrow band of damage running across it. It's too wide for a wire cut, the width and the evenness of the damage looks like a rope to me. I can't imagine how you'd tie a rope at that angle, so I'm thinking this rope was tied to something else and the horse caught it on her leg.
The only thing I'd like to mention is that if you do wrap it, the recommendation is that you wrap both legs of a pair (both front, or both back) even if there is only an injury on one leg.
I've heard that about things like bowed tendons, so I'm thinking maybe it has to do with making the horse move stiff on one side but not the other. I had one get a BAD cut in the same location as these on a front leg and the vet showed me how to bandage it, but never said a word about doing it to the other. Most likely because the wrap didn't go across any joints, just around the pastern.
