I've had cats all my life (at least two and at times 3). I got my first dog 4 years ago. She's a border collie mix and had been around cats. However, she still barks and will chase a cat up the street if she sees it yet pays no attention whatever to the ones living w/her. She seems to know they are part of the deal and just ignores them. My cats took about a week to settle w/it but never hissed or clawed Mickey. They did stay up on their perches a bit more but after about a week, they pretty much ignored her as well. That's my experience anyway.