The side view of your horse should have a small ridge where the withers are. If you horse just has a gradual slope toward the rear without any shoulder definition, you have a mutton-withered horse. The thocratic vertebrae which usually create extra shoulder definition are shorter than normal. This is most common in American Quarter horses, ponies, and arabians. Your horse will probably have less of a range of motion because of the mutton withers, but will perform as well as other horses.
The problem that mutton withers create in saddle fitting is that most saddles are built with normal withers in mind. The withers help keep the saddle in place, creating a ridge.
Important Points to note while saddle fitting a mutton-withered horse:
The first thing we'd recommend for a mutton-withered horse is a saddle especially designed for your horse's conformation. We have a few options. Many of these are designed for halflingers, which have flat top-lines and shorter backs, but these saddles will also work for mutton-withered horses with normal back lengths. Try out our newest option, the Big Horn Flat Top-Line Saddle. We also frequently recommend the Big Horn Halflinger Cordura Saddle, Big Horn Mutton-Withered Saddle, or if your horse has a wide back, the Big Horn Extra Wide Trail. The trees on these saddles do not depend upon the withers to keep the saddle in place and evenly distribute your weight without putting too much weight in the front or back.