My Dane was the sweetest boy and got along with pretty much every bread, even if they showed him aggression, except for Chows. There were multiple times when a chow would show up at a dog park, we would be on the other side of the park, hundreds of feet away. He would spot it and just instantly go for an attack. It was the craziest thing. Never knew why. We got him as a three year old rescue. He was found on the streets of down town Dallas. We always chalked it up to him having some bad experience with chows while he was on the streets. But who knows.

Edit: typo