I have a male mini schnauzer too and had the exact same issue you did. he got and killed 7 chicks of mine when they were just a week old. He didn't eat them, just killed them. I have a couple of silkies in a dog proof brooder in the house right now and he will sit and stare at them for hours just shaking. I have tried various behavior modifications without any luck. He isn't nutured yet either. They only solution I came to was to keep him separate from the chickens. My son's yellow lab goes out to the coop to help me take care of the chickens everyday and have never had any problem with her. She just ignores them as does my rotti. Must be something in the schnauzer breed.