Actually, it is covered just below in P (here if the full context). Also, you need to view both the Saddlebred SB) rules and General Rules (GR) for complete rule context:
Soring and/or the use of an action device on any limb of a Tennessee Walking Horse, Racking Horse, or
Spotted Saddle Horse (each a breed not recognized by the Federation) in any class at a Federation
Licensed Competition is prohibited. An action device is defined by the USDA as any boot, collar, chain,
roller, or other device that encircles or is placed upon the lower extremity of the leg of a horse in such a
manner that it can rotate around the leg or slide up and down the leg so as to cause friction or strike the
hoof, coronet band, fetlock joint or pastern of the horse. (Protective bell boots or heel boots are
specifically excluded from this definition). The use of a weighted shoe, pad, wedge, in conjunction with a
hoof band or other device or material (commonly referred to as a performance package) placed on,
inserted in, or attached to any limb of a Tennessee Walking Horse, a Racking Horse, or Spotted Saddle
Horse (each a breed not recognized by the Federation) constructed to artificially alter the gait of such a
horse, and which are not protective or therapeutic in nature, at a Federation Licensed Competition is
prohibited.
p. Soring of any horse, including but not limited to the application of caustic chemicals to a horse’s legs or
hooves, in order to cause pain and/or affect a horse’s performance, and/or used as a training technique.