As far as the secondary poisoning goes (chicken/cat/dog eat dead poisoned mouse), it really depends upon how many poisoned mice the animal eats & how big the animal is. If a chicken or a cat eats only one poisoned mouse, or maybe two within a short time-frame, there's a slim chance of them getting sick. The poison the mouse ingests is designed to kill a mouse based on it's body size. It also depends on what the poison is. If it is a fat-soluble poison, it gets stored in the dead mouse, and can be transfered to larger animals. However, it'd take a lot more poison to kill a chicken or cat than it does to kill a mouse. And it takes even more to kill a dog. Unless you have a massive influx of mice and their little bodies cover the coop or yard, and your chickens aren't getting enough protein in their regular diet, you won't see any impact on your flock, especially if they have a wide array of food choices. However, if you've got rats & your chickens like to eat them, you would have a higher chance of getting your birds poisoned because rats are so much larger than mice & it takes a stronger poison or more poison to kill them. I feed my girls 20% protein crumbles and they free-range throughout the yard. I've had mice bait stations hidden in locations the birds can't get to since May 2010, and I've found dead mice in the yard. I've not had a single problem with my four girls exibiting any signs of poison. If you keep the dead mice cleaned up, you won't have a problem. Also, the nasty smell of dead creatures is present whether you poison or trap, you just need to be on top of cleaning them up, especially in an enclosed coop.