Sorry, I should have mentioned...the rat kill was only a result of the whole chicken coop and run being revamped to prevent rat access to food and to remove rat habitat. The removal of the debris under which the rats were living is what caused the rat to start running around in broad daylight, which is what resulted in my dog catching him.
We put hardware cloth underneath the coop and removed all the composting leaves and the yard waste bucket that they were living under. I still need to remove the bricks that they dug under.