I don't know if this was asked or answered yet. Does he Kill maliciously or over playfully? I had a lab that killed a few of the barn kittens. He was just too rough with them. Now that he is older and the cats can fight back nothing has happened. If he is killing for the maliciously you aren't going to stop him. If he is just too rought and unintentionally kills you may be able to fix with proper obedience and training. My lab now can be left with the cats and any of the birds. Plus all my dogs love the goat! I really wish you luck. These things are hard. My boxer killed and ate one of my hens earlier this year. I was torn with what to do. But working with her and teaching her that chickens were off limits helped me.