Years ago when my wife and I started to raise chickens we struggled with mice in the coop. Yes our birds did their best at controlling them. The chickens were catching mice daily, but, we still were finding a lot of mice. And I was getting tired of patching the holes in the coops wall that the chickens were making trying to get at the mice in side the coops walls. We came up with the idea of raising a pair of kittens in the coop and run with the chickens. The cats are fully accepted by the chickens and will lay down with the cats in the run. As for the cats, one of them will greet the hens with a head butt while the other treats them no different than any other two legged animal, total indifference. The only time I've seen any aggression towards the chickens from the cats is when the birds try to take the cats kill, than its just a quick bat with their paw. As for the mouse problem, they are so rare how that the cats have taken to leaving the run to catch mice, rats, squirrels and drag them back into the run to kill. As for the snakes, since the cats we have only one. a large bull shake. We've seen it in the coop several times over the last few years. Haven't lost any birds, maybe a few eggs, but, otherwise no problems from that one.