Answer

By Your Horse

Instructor Jane Baker advises:

I would guess that he’s in some pain. Often these problems start in a subtle way, perhaps initially due to a slip, fall, or an awkward jump. In many cases, the pain is due to an incorrectly fitted saddle or bridle – or perhaps a foot balance issue has caused the horse to adapt his way of moving to prevent further discomfort.
The problem shows as stiffness or resistance and can lead to behavioural issues if left.
I suggest that you get the horse’s teeth and back checked. Also ensure that his feet are correctly shod and that you have the fit of his saddle checked.
Get an instructor to watch you ride – you may not be sitting straight or could be stronger on one side. Either problem will cause the horse to compensate and, therefore, move differently.