Were we to select the perfect withers for our mounts with the idea of arranging the best possible fit for the saddle, we would probably settle on well-placed, prominent withers that blended nicely into the slope of the shoulder and the back. However, the shape of a horse’s withers with regard to saddle fit is complex. “Your average horse’s withers will involve the fourth through 10th thoracic vertebrae,” says Joyce Harman, DVM, MRCVS. Yet in some horses, this bony ridge will be longer, while others are shorter.
Nevertheless, it is the individual conformation differences in the neck, back, and shoulder areas of each horse that gives rise–or possibly no rise–to the shape of his withers. And because of the various sizes and shapes withers can take, they have always been one of the biggest challenges in fitting the saddle to the horse.
“A major complicating factor in saddle fit is that horses can and do change shape in the saddle-bearing area countless times over a lifetime, especially across the withers,” says Harman. For instance, the shape of your horse’s back and withers was narrower in his youth. Now in his prime, he exhibits a wider back with more fully developed muscles along the withers and into the shoulder. By the time he’s 15 years old, his back will start to sway a little and the muscles around the withers will atrophy to some degree, creating longer, narrower withers.
As a result of your horse’s aging, the saddle that fit perfectly on the 3-year-old you started four years ago probably won’t fit that same horse quite as well now that he’s seven.
Changes in the character of the withers can develop rapidly, too. Horses that are put into serious competition or work might start out heavier and wider while they are out of condition, but by mid-season they will have lost some fat in the topline and added muscle in t