Wyo. Stat. § 37-9-305
Any corporation operating a railway and failing to fence the same and to construct and maintain suitable cattle guards as required by W.S. 37-9-304, shall be liable to the owner or owners of any livestock killed or injured by reason of its failure to construct or keep in repair the fence or cattle guard in the manner provided in W.S. 37-9-304, for the full amount of the damage sustained by the owner on account thereof and to make a prima facie case for recovery, it shall only be necessary for the owner to prove the loss or injury to his property; provided, that no corporation operating a railroad shall be liable for any damage occasioned by the willful act of the owner or of his agent or employees or for stock killed or injured on public road crossings unless negligence on the part of the corporation, its agents, servants or employees can be shown.
W.S. 37-9-305