14,000 years of being domesticated to serve as companions for humans is the inherent reason that works for me. Cows or pigs don't have the same history of domestication to be companions. Dogs share a special bond with humans and a special place in our society. Rightly or wrongly, and admittedly cows and pigs suffer to certainly the same extent that any factory farmed animal suffers, dogs serve a different purpose.

Given this history and bond, to eat or put dogs in danger is in my mind almost as morally objectionable as putting a person in grievous danger against their will.