I have 6 barn cats, and none of them have ever killed any of my chickens. I have a hen that lost an eye to a cat scratch, but I'm sure the hen started it. She kept laying eggs in their food dish. When she went broody, she sat in their dish and would attack them when they came near. DH and I had been removing her from the dish and trying to break up the broodiness. We eventually had to put her in a cage, but not before one of the cats had to defend itself.