Low-withered horses, also known as mutton-withered horses, are those with sloping backs caused by underdeveloped slopes between the shoulder blades and the neck. Horses like this have no noticeable shoulder definition which can cause saddle slipping or rubbing by the front. Normal saddles can also pinch their backs because of the lack of wither definition.
A gel saddle pad like the Front Riser Anti-Slip Gel Pad works best for low-withered horses because it balances out the ride by providing extra padding on the front. It is also ideal for horses with high withers BUT are lacking muscle definition behind them.