If the toes are squared that puts a lot of stress on the toe quarters. Usually with a long overstride, the hind clips the bulbs of the front. Watch the horse move directly away from you to see if it isn't a hind striking the other, especially if the horse is base narrow.
called forging....at times its just laziness on the horses part. similar to the term "dragging your feet"....if your riding and they are forging just speed up the front end. gets their front feet moving a little faster to get outa the way of the overstepping rear.
if you trim the hinds shorter it just speeds them up even more. doesnt help the problem........
Sounds more severe/exaggerated than normal, if that's correct.
1. Ensure his feet are in good, functional form & balance. See e-hoofcare.com for starters.
2. Ensure his body is in good functional form & balance. It is common for horses to have progressive hind end issues, even in absence of injury or damage from being worked to young or such. Best chances of rehab are addressing it when the horse is still immature. See a good veterinary chiropractor or such.