Could be anything. I had one that did this for the longest time
and it turns out he had OCD in his right rear stifle. My guess is that he was
relieving back tension from carrying himself in an unbalanced fashion due to
the painful stifle. He compensated really well for it for a long time (2 years
that I had him). I knew something wasn’t quite right because he was unbalancing
that hoof ever so slightly and we never could get it to stay completely
balanced. Finally after 2 years of not feeling comfortable putting him on a 50
mile ride, I had a really thorough vet exam done.
