Saddle Fit Basics in Four Parts - Spinal Clearance
To many it will be obvious that the saddle can not make contact with the horse's spine, especially the wither. A saddle sitting directly on the spinal column (remember these are bony structures) will cause the horse to be very painful and sore and he may refuse to work or act out with bucking/rearing/bolting as a result of this pain. However, once we have clearance what would "adequate clearance" entail?
I've heard lots of rules of thumb in the past, whether it be 2 fingers, 4 fingers clearance over the wither. Others say, just as long as it's not touching you're fine. What's important to consider is if you evaluate your spinal clearance in the aisle with the horse standing statically, you don't have the added factors like a properly tightened girth, the weight of the rider, or the movement/lift of the horses back to consider. Thus the best way to evaluate will be with a rider mounted and the horse in motion.
To get a general base, I do start in the aisle preferably with no pad and the saddle girthed down. What I'm looking for is room to get my hand down the gullet to the base of the wither (assuming the saddle is placed properly with the tree points either directly behind the scapula for a Stübben, or slightly further back for other models, depending on the manufacturer) which is especially important for a horse with a very long wither. We don't want to have clearance at the pommel and then make contact halfway down the gullet since this will still make the horse sore.
In addition to having clearance over the top of the wither, I also want to make sure I have some room on either side as well. It's difficult to see in the picture above, but I can put two fingers on either side of the wither with room before the panel makes contact (I would call that adequate). What people often forget is that the spinal cord and wither is very mobile in the horse and needs to be allowed to move freely side-to-side. If the saddle is too tight on either side, it will restrict the horse's movement and may appear lame or just unwilling to move out and forward.
Notice, I specifically haven't mentioned an exact measurement over the top of the wither for proper clearance. That is because the necessary amount of clearance will vary from horse to horse. In general, I would like to have at least 3-4 fingers clearance over the top of the wither with the saddle girthed and rider mounted to account for the horse's movement, compression of the flocking, and other factors depending on the individual case. However, if I'm dealing with a downhill or mutton withered horse, the amount of clearance may be higher to allow proper balance of the saddle from pommel to cantle. It may look funny to have a lot of room but we'll talk more about how important the balance of the saddle can be on those horses. Essentially if all the other factors are adequate, you really can't have TOO much clearance, but you definitely can be too close to the spine.
This picture above would be a prime example of a saddle with proper clearance above (I have room for roughly 4 fingers), but not at the sides of the wither (I can't even get one finger next to the side of the wither). I would expect this horse to be restricted in his movements. He may not present as totally sore, but may be less willing to move forward and work than he would in another saddle.
|U shaped tree|
|V shaped tree|
Excuse the poor artwork but the pictures above are a rough illustration of two common types of tree shapes shown as a cross section of the horse's wither with the head plate/gullet plate shown on top. The V shaped tree on the left is the most common shape you'll find in a saddle, while it can fit just fine on the shown horse's cross section we are a bit snug on either side of the wither and do not have even contact through the point. In this situation, it may be necessary to go wider with the tree size and add extra padding or a half pad to offer proper clearance, just to allow freedom of movement.
On the right, I show a rough drawing of the shape of a Stübben tree. You can see that there is more room on the sides of the wither (still keeping clearance over the top) and the tree points are making more even contact with the horse's side for better bearing surface of the tree. In general I prefer this method of fit, though some horses can work fine in V shape tree I tend to find better comfort and results in a U shape instead.
To recap: we don't want the saddle coming into contact with the horse's spine especially on the top and sides of the wither. Adequate clearance may vary from horse to horse depending on his build, but should be reevaluated with the saddle girthed down and rider mounted to ensure proper clearance. When in doubt, call a certified saddle fitter to help evaluate your horse and take other factors into consideration.
Coming soon, Tree Width, Balance/Stability, Bearing Surface, and other notes!