I have the original Dyson Animal and now hate it. It weighs a ton and doesn't suck that well.(go figure....) I just bought the cheaper Dyson DC25 Ball and it's like night and day. My Animal is a DC14 (the most powerful one they made at the time) and this one is ten times better, but still pricey, over $400. We have two Shih-Tzu's that I now keep cut short but they still like to roll and also have long tail hair and ear hair so it's still an issue.
I would say that your filter is dirty or you have something stuck in one of the air channels.
I worked at Sears when Dyson first hit the market in the US - and it truly is an incredible vacuum cleaner.
We have a Dyson - and as long as you keep the filter clean - and the air channels open - you won't have a bit of trouble.
If you own an animal that sheds- you need a Dyson!