Mo. Rev. Stat. § 430.030: Lien, for labor or material furnished, on horse, mule or other animal.

1. Every person who furnishes labor or material on any horse, mule or other animal, who shall obtain a written memorandum of the work or material furnished, or to be furnished, signed by the owner of such horse, mule or other animal, shall have a lien for the amount of such work or material as is ordered or stated in such written memorandum.

2. Such lien shall be on such horse, mule or other animal as shall be placed in the possession of the person furnishing the labor or material; provided, however, that for labor and material furnished on more than one horse, mule or other animal belonging to the same owner, the person furnishing such labor and material may, at his option, have a lien on any one or more of such horses, mules or other animals for the amount of labor and material furnished on all of such horses, mules and other animals belonging to such owner.