I had a rat that was digging into one of my runs and eating the remaining crumbles every night. I feed mine usually twice a day, if I'm not working 12+ hours a day. I put just enough in there so they will get plenty to eat but not have much left over. I put some rat poison out, big green balls that are fish flavored. I counted the balls so I could pick up any that were remaining so the chickens wouldn't eat them when they're out. I also set some of those LARGE wooden rat traps and staked them to the ground with a string. I tried peanut butter for a few nights with no luck. Then I put a big piece of balled up bread on the trap.I caught a huge field rat. Just the body was about 10" long! If it's mice you can make one of those 5 gallon bucket water traps. All you need is a bucket, a large vegetable  can or coffee can and piece of 1" PVC pipe. You can google how to make one. I saw a video online where a guy had chickens and had a pretty bad mice problem. He caught about 30 mice the first night.