Wither clearance is an often misunderstood concept
All of us are concerned that our saddles have adequate wither clearance and do not pinch our horse’s withers. But few of us truly understand exactly what “wither clearance” means.
Many of us learned in Pony Club that our saddle should have 2-3 fingers clearance on the top of the withers. But we were never taught that there also had to be clearance on the sides of the withers. One of the reasons this is crucial is because when the horse moves, his shoulder blades rotate upwards and backwards. The saddle must have an opening (clearance) on the sides of his withers to accommodate the shoulder rotation.
To see just how much your own horse’s shoulder blade rotates backwards when he moves, stand on the side of your horse and mark the shoulder blade with a piece of chalk. Then have a friend stretch your horse’s front leg forward and mark the new position of the shoulder blade. You will see how much farther back the shoulder blade is now positioned.
Ideally, we should be able to get 2-3 fingers clearance on both the top and the sides of the withers. To determine adequate clearance on the sides of the withers, we measure from the point just above where the stuffing of the saddle starts. On a mutton-withered horse, however, we may get as much as 4-5 fingers clearance.
If there is no clearance (or space) on the side of the withers, the horse’s movement will be restricted. It will be impossible for him to have free range of movement through his shoulders.
A horse whose saddle pinches his withers may be reluctant to go forward. Other more extreme signs of insufficient wither clearance are patches of white hairs (not scattered individual white hairs) or sores on the top or on one or both sides of the withers.