Leo Walker
Well-Known Member
IME, if there has been a behaviour change with no other changes, it's almost always due to pain. Though there are plenty of strong, determined trainers who can often persuade a horse to work through pain, which can make it look like it was a training issue.
I know a pony that had mounting issues. It was sent away for schooling to a reputable yard, so no harsh treatment but it was given no option other than to get on with it. Turned out it had a fractured pelvis the whole time!