There is a certain poison that states other animals can eat them without secondary poisoning. That being said, would you feel okay eating the meat or eggs from a chicken who has eaten a critter that died from poison? I sure wouldn't. I use a bucket trap to catch pesky rodents. Fill a 5 gallon bucket half full with water, then cover the surface of the water with sunflower seeds so it looks like its full of seeds. Provide the nasty little critters with an access ramp (I lean a board against the side of the bucket). They jump in for the seed, and can't get back out and drown. I put the trap up just after I close the chickens in for the night, and remove it before I let them out in the morning. Chickens like sunflower seeds too. I guess if you wanted you could feed them to your chickens, but I just burn them. I keep resetting the trap every night until I don't catch mice in it anymore. Or- you could just get another cat. Good luck....