There are a lot of opinions out there where exactly a saddle should sit correctly, and it may depend somewhat on the discipline you are riding in, the fact remains that the saddle should stay off the shoulder and be placed before the 18th thoracic vertebra. This is what is called the ‘saddle support area’ (SSA) and is relatively simple to find on your horse. It’s sometimes surprising how small this area actually is even on what seems a long-backed horse, and as the horse matures, it can actually grow smaller as the shoulder muscles grow larger and move the shoulder blade further back.
The SSA begins about four fingers behind the base of the withers (making sure that the tree points are always behind the back edge of the shoulder blade) and ends at the 18th floating rib. You can easily find this if you follow the hair line up to the spine and feel where the lumbars begin and the ribs end.
You want to make sure that your cantle is slightly higher than the pommel, and that your billets (short or long) are hanging down perpendicular to the ground. Since your girth will always gravitate to the narrowest part of the chest under the elbows, it could happen that the pressure on the billets will pull the saddle forward over the shoulder during movement. This could cause damage to the sensitive shoulder cartilage over time.
Conversely, if your saddle ends up sliding back into the sensitive lumbar area, this could hit the reflex point which causes bucking, or it could cause the horse pain in its kidney area or at the ovaries. You want to make sure that the girth is tight enough to prevent slippage, but of course not so tight that the horse can’t breathe!
Your horse will tell you if he’s comfortable – as the rider you will feel whether he responds readily to your aids, or seems resistant because something may be ‘off’.
Author of ‘Suffering in Silence - The Saddle fit Link to Physical and Psychological Trauma in Horses’ (2013) Jochen Schleese teaches riders and professionals to recognize saddle fit issues in Saddlefit 4 Life lectures and seminars. We help you find answers in a personal 80 point Saddle Fit Diagnostic Evaluation.