Well, I've been thinking about this, and perhaps there ought be no law. However, because I believe that animals are neither persons nor property, but another category of being, one I'm not prepared to fully define here, I think perhaps animal cruelty should be a defense for one who removes an animal from its current master, even if to do so that one harmed the master. In other words, government forces cannot be brought to bear against you for animal cruelty, but your protection from the law, in regards to that animal, is reduced.
It basically means, if you're torturing your dog and I knock you over and take the dog, I can cite your abuse of the dog as a defense against both civil and criminal proceedings against me.