Whenever any livestock shall be injured or killed by any railroad, so as to render the railroad liable under section 537.270, or otherwise, and the owner of said livestock so injured or killed, or his authorized agent, and the agent or adjuster of the railroad, shall agree upon the amount of damage or damages sustained by the owner, the railroad shall, within forty days after said agreement, pay to the owner thereof, or his authorized agent, the amount of damage or damages so agreed upon.