California Code, Penal Code - PEN § 597n

(a) Any person who cuts the solid part of the tail of any horse or cattle in the operation known as “docking,” or in any other operation performed for the purpose of shortening the tail of any horse or cattle, within the State of California, or procures the same to be done, or imports or brings into this state any docked horse, or horses, or drives, works, uses, races, or deals in any unregistered docked horse, or horses, within the State of California except as provided in Section 597r, is guilty of a misdemeanor.

(b) Subdivision (a) shall not apply to “docking” when the solid part of any cattle's tail must be removed in an emergency for the purpose of saving the cattle's life or relieving the cattle's pain, provided that the emergency treatment is performed consistent with the Veterinary Medicine Practice Act (commencing with Section 4811) of Article 1 of Chapter 11 of Division 2 of the Business and Professions Code.

(c) For the purposes of this section, “cattle” means any animal of the bovine species.