How to Fit a Saddle to the HorseBalance
The center of the saddle (seat area) should be parallel to the ground while on the horses back with the pommel slightly lower than the cantle of the saddle. If the balance of the saddle is tilted so that the pommel is higher than the cantle (saddle that is too narrow), the rider's weight will fall onto the back of the saddle and it will force the rider behind the horse's natural motion. If the saddle pommel is too much lower than the cantle (saddle that is too wide) the rider's weight will onto the front of saddle and it will force the rider in front of horse's natural motion. Either scenario will leave the rider fighting the saddle to stay in proper balance and it will leave the horse suffering from an imbalanced rider that is putting too much weight in either the front or back of the saddle.
The clearance between the pommel of the saddle and the horse's withers should be 3-4 fingers, for normal withers. Horses with mutton withers (little to no withers) will have slightly more clearance, while horses with high withers will have slightly less. It is important to ensure that horses have clearance all around their withers and not just on the top. Not having the right amount of wither clearance will affect your saddle balance. Having a saddle without sufficient wither clearance (Gullet too wide) will result in you sitting too low on the top of the horses withers and apply too much pressure on the top of withers which will lead to rubs or cuts on the top withers. A saddle with too much clearance (Gullet too narrow) will leave you sitting too high up on the base of the horses withers and apply too much pressure on the wither base which will lead to rubs and white hairs on the base of the withers.
The channel of the saddle (space between the saddle panels) should offer adequate clearance over the spine and connective tissue throughout the entire length of the saddle. It is often one of the most overlooked aspects of saddle fitting. A channel that is too narrow will impede the horse's movement dramatically and may even cause the spine to be visibly sore. Feel the width of your horse's spine and it's connective tissue with your fingers to estimate it's width. The channel of the saddle should completely clear this width and rest on the long back muscle of the horse's back.
The panels of the saddle should have even contact and pressure with the horse's back all the way from the front to the back of the saddle. The front panel should not pinch the withers in any area. Saddle bridging occurs when there is a space near the center of the saddle where the panels do not make good contact with the horse's back. This will cause the saddle to rock forwards and backwards. Some saddle brands are designed to sit off of the horse's back at the end to allow the horse's back to come up during hind end engagement.
The saddle must be in proper proportion to length of the horse's back. It is essential in removing any possibility of undue pressure in the wrong areas of the horse's back. The shoulder and loin areas should not carry any of the saddle or rider weight. The rider must be placed centrally in the saddle seat on the saddle support area to allow perfect balance, free movement, and to maximize the bearing surface on the horse's back. If your saddle is too long for your horse's back it will sit too far back and rest on the horse's loins, cause pressure, discomfort and inhibit free movement. Saddles with gusseted panels will put pressure out further then the seat of the saddle making the overall length of the saddle longer. Some saddle brands use non gusseted panels that cup under the seat of saddle allowing the saddle to sit shorter on the horse's back then the length of the seat. This must all be taken into consideration especially with a short backed horse.