Missouri Revised Statutes Title XVII. Agriculture and Animals § 270.170. Swine or sheep taken up--notice to owner--considered feral hogs, when

1. If any swine or sheep 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 or sheep shall be found to restrain the same forthwith, and give the owner, if known, notice in writing that such person has restrained said swine or sheep, and the amount of damages such person claims in the premises, and requiring the owner to take said swine or sheep 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 or sheep.  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 or sheep be unknown, such swine or sheep shall be disposed of in the manner provided for in section 270.180.

2. Any swine not conspicuously identified by ear tags or other forms of identification that were born in the wild or that lived outside of captivity for a sufficient length of time to be considered wild by nature by hiding from humans or being nocturnal shall be considered feral hogs.  Any person may take or kill such feral hogs on such person's own property.