Mo. Rev. Stat. § 267.430: Diseased animals — sale or running at large prohibited.

A person shall not sell or offer for sale, or run at large on any common or unfenced lands in this state, any livestock affected with a serious external parasitic infestation or any infectious or contagious disease whatsoever; provided, that this section shall not be so construed as to prohibit the movement of such infected animals under conditions prescribed by the state veterinarian for the purpose of segregation or quarantine, or for immediate slaughter under state or federal inspection.