We were given two cats once. One took up living in the chicken yard. Great mouser, never bothered a chicken or a chick. Later when both of those were gone we got a kitten to be a mouser. She was great. We have an electric netting fence around our chicken yard so we thought she would just stay out. Once chicks were born she became determined to get in and used the wood pole at the gate to do so. All my efforts to stop that failed because she was a very determined cat. She would even let herself get shocked in order to get in. I had to have her re-homed. Cats are different. No one individual experience with cats or dogs can be the rule for all cats or dogs. While it seems unlikely a cat will kill a grown chicken I wouldn't rule it out. Any cat that is a small animal hunter will likely kill chicks. Grown hens and roosters will probably not be able to stop that.
I asked an old timer once what to do about a dog that killed chickens. The only advice he offered was to kill the dog. Once upon a time when people were dependent on their livestock for food they wouldn't think twice about killing any predator that threatened their livestock. But now that people are not dependent on their flock and keep them as pets as much as for food, it becomes harder for people to make that choice. I am sure in most rural areas however it is still OK to kill any dog or cat on your property that is killing your livestock. Our electric netting fence mostly eliminates the danger and thus the need to make that choice. However a small determined cat could get through at the bottom and a large determined dog could just rumble over. And the electric netting is pretty pricey. We got ours after two dogs went on a rampage and killed 30 of our chickens. While it is not a guarantee it does provide us with a lot more protection.
