Colo. Rev. Stat. § 40-27-105
The killing or injury of any animal by a railway company or corporation shall be prima facie evidence of the negligence of said railway company or corporation, and every railway company or corporation in this state and every assignee or lessee thereof shall be liable to pay to the owner the full value of each animal killed and all damages to each animal injured by the engines or cars of such railway company or corporation in this state or the assignee or lessee thereof unless the railway company or corporation, by competent evidence, shall affirmatively show that such killing or wounding was not caused by the negligence of such railway company or corporation or the assignee or lessee thereof. On the trial of all actions for damages arising under this article, in order to admit evidence of absence of negligence, the defendants shall first be held to show a compliance with sections 40-27-102 to 40-27-113 in relation to the erection and maintenance of fences, gates, and cattle guards.
C.R.S. § 40-27-105