Is it possible to use a flash under those conditions? I would think the slightest pop from your flash would put a nice catch light in the dogs eyes, I think all animal shot need some reflection in the eye.

I also think you should try to shoot a little lower. Get a good monopod and it's simple to shoot at eye level. I'm not sure it that's what people want, but I believe at or just below eye level is the most interesting and realistic. Angle down shots from above the animal puts them in a less flattering position.

Overall you did capture well exposed images. If you can shoot a flash, try slowing your shutterspeed and selecting rear curtain sinc and do some experimenting. . .

Good luck.