Nice shots. As a point I prefer dynamic point to 3d tracking for this kind of subject, but thats just me. What aperture were you at? If you find the depth of field too small (ie to help with focus issues or bring both dogs into focus in the first one) you could always close that down.
I ran them through Photoshop to brighten them a bit
Yeah, in the bright snow, the camera will read it wrong and want to underexpose your images, so you'll need to use manual mode or dial in some exposure compensation. Best bet is to dial in your own exposure in manual mode once you have a spot on exposure.
As for the composition, I think you may have been better off crouching down to a the dog's level for a different perspective and to get in some background rather than just white snow, it looks a little as if we're always looking down on the dogs.
Nice effort though!