We have an Akita and Alice gets along wonderfully with her.
Here's just a thought that immediatly popped into my head when I read this - you said they are fine with a Great Perinese, that's a dog WAY bigger than a boxer or pit bull.
Are YOU nervous around boxers and pit bulls?? If you are concerned about dogs with those features (it's very common for people to be nervous around pit bulls especially since they have a bad rep) then you are most likely transfering your own nervousness to your Yorkies. That's my number one guess as to what's happening whether you notice it or not, just based on the way you described "dogs with those type of features".
Dogs don't descriminate against other dogs based on looks, it's the temperment and energy that dog gives off, so another possibility (if YOU're not worried about these breeds) is that it's just their excitemnet level. Pits and Boxers tend to be high energy dogs (Perinese (sp?) tend to be mellow), so even if the dogs they've met are friendly, it could be that they seems too hyper to your Yorkies and they don't like that energy. |