Oh, I know it.
Rotties can either be big, dumb and lovable or big, dumb and vicious. Usually it's the owner that makes or breaks the dog.
Except for the one that attacked me years ago. That dog had mental problems from in-breeding and even the greatest owner in the world couldn't have changed that dog's aggressive behavior.
The dog was only 9 months old and so vicious, it turned on its owner.
There are some dogs that just love killing chickens though. It's like it is in their blood. They may be the gentlests of beasts but when they see "chicken".....I had one like that. He didn't specialize though. He liked rabbits, kittens, and hamsters too but chickens were his favorite. (notice the emphasize on had and were:')