Mo. Rev. Stat. § 267.450

It shall be unlawful for any person, firm, company, or corporation, owning or operating any stock pens or stockyards in this state, to permit any livestock, cattle, hogs, sheep or goats, not under or subject to quarantine, to be unloaded into any pens, enclosures, or yards, wherein any quarantined livestock is, or has been kept, or into such pens, enclosures, or yards, under such conditions and circumstances as will render such livestock subject to quarantine, and thereby prevent immediate removal thereof from such pens, enclosures, or yards, if the owner or shipper shall so desire.