Sore

Sore when used to describe a horse means:
(1) An irritating or blistering agent has been applied, internally or externally by a person to any limb of a horse,
(2) Any burn, cut, or laceration has been inflicted by a person on any limb of a horse,
(3) Any tack, nail, screw, or chemical agent has been injected by a person into or used by a person on any limb of a horse, or
(4) Any other substance or device has been used by a person on any limb of a horse or a person has engaged in a practice involving a horse, and, as a result of such application, infliction, injection, use, or practice, such horse suffers, or can reasonably be expected to suffer, physical pain or distress, inflammation, or lameness when walking, trotting, or otherwise moving, except that such term does not include such an application, infliction, injection, use, or practice in connection with the therapeutic treatment of a horse by or under the supervision of a person licensed to practice veterinary medicine in the State in which such treatment was given.

Source

9 CFR § 11.1

Scoping language

For the purpose of this part, unless the context otherwise requires, the following terms shall have the meanings assigned to them in this section. The singular form shall also impart the plural and the masculine form shall also impart the feminine. Words of art undefined in the following paragraphs shall have the meaning attributed to them by trade usage or general usage as reflected by definition in a standard dictionary, such as Webster's.