Mo. Rev. Stat. § 430.150: Lien for keeping or training horses and other animals.

Every person who shall keep, board or train any horse, mule or other animal, shall, for the amount due therefor, have a lien on such animal, and on any vehicle, harness or equipment coming into his possession therewith, and no owner or claimant shall have the right to take any such property out of the custody of the person having such lien, except with his consent or on the payment of such debt; and such lien shall be valid against said property in the possession of any person receiving or purchasing it with notice of such claim.