Mo. Rev. Stat. § 270.170
If any domestic swine shall be found running at large, contrary to the provisions of this chapter, it shall be lawful for any person on whose premises said swine shall be found to restrain the same forthwith, and give the owner, if known, notice in writing that such person has restrained said swine, and the amount of damages such person claims in the premises, and requiring the owner to take said swine away and pay such damages; and such owner shall pay such person a reasonable sum for taking up, feeding and caring for the same, and the actual damages done by said swine. If such owner fails to comply with the provisions of this section within three days after receiving such notice, or if the owner of such swine be unknown, such swine shall be disposed of in the manner provided for in section 270.180.
§ 270.170, RSMo