You've either got to add another light or reposition what you have...or use a much larger light source closer to the animal to get the light to wrap more. Of course any of these options changes everything.

With cats I use medium and large softboxes to wrap the light and if I have a real problem I'll add another light to eliminate the shadow...makes for flat lighting so I don't like to do that. Also the problem is not as pronounced in cats because the muzzles are very short compared to a dog snout.

I still end up Photoshopping more than I want.