Ran across this interesting video of a racetrack farrier patching a quarter crack in a hoof. It shows quite a lot of detail. I’ve seen the procedure done, but never quite this close up before.
I ran across it in a blog post about a barefoot endurance horse that had a hole in the hoof, and they applied a slightly modifed version of that patch. Be interesting to see if it holds up on a hoof that has more expansion happening than the shod racehorse.