Mo. Rev. Stat. § 270.210

If any stallion or any unaltered male mule or jackass, over the age of two years, be found running at large, the owner shall be fined, for the first offense three dollars, and for every subsequent offense not exceeding ten dollars, to be recovered by civil action before an associate circuit judge, in the name of any person who will prosecute for the same, one-half to his own use and the other half to the use of the county.