Peter Singer is 'the godfather of animal rights' or whatever and he has a metric for ethical chicken farming, like a certain number of chickens raised per acre, free range.
It's way fewer chickens than currently raised but I think that's an interesting way to think about it...if we didn't have demand for eating chicken, many of these chickens wouldn't exist. Is that better than living a close-enough approximation of your wild life? Kind of a hard question.