We've had rotts in the family (I haven't owned one), I know atleast three while we had chickens. One sister had two, don't remember the female messing w/ them the male (mix) did once and they broke him of it. Another sister had one and he was a chicken and cat killer. I did manage to break him from bothering the cats (but only cats he knew), and he got better around the chickens, but I never fully trusted him.
I agree w/ it being how they are raised, I tried to tell my sister when hers was still a puppy that she was going to have trouble w/ him around cats, he was just way to rough. Her thoughts on it were she didn't plan to have cats or chickens so it didn't matter, well guess where he ended up? With us! And he had to live on a chain. After he got sick we moved him inside. I know he sounds terrible, but he was really a nice dog, w/ the cats he just didn't understand his own strength, I don't think he intended to kill them.