Input per req:
1. I really like this image, and the mood, my only thought is that what I assume is the dog's tail is resting on his muzzle and is slightly confusing to the eye. It also doesn't seem quite level to me.
2. This isn't a good pose for a dog; the foreshortening of the muzzle puts it out of scale to the rest of his body. Animals and people are generally best shot at eye-level; get down and shoot toward him, ideally with a 3/4 profile and him looking at you. In this pose, he appears to be laying down on a very steep slope and I keep wondering why he doesn't slide down. Good use of the sheet(?) to make an even background, but watch the wrinkles.
3. Nice idea, but at least 2/3 stop under-exposed, and as mentioned, much of his detail is lost in the background. I would suggest reshooting this one, set the dog further away from the background (to allow for a shallower DoF and a softly focused background) and the use of a fill light image right to illuminate this back.
Some nice work here, but with room for improvement. I'm not an animal photographer, but I feel that generally they're best captured out of doors, rather than in studio portraits.
Just my $00.02 worth - your milage may vary.
~John