The Ethics of Killing Animals

While it is generally accepted that animal welfare matters morally, it is less clear how to morally evaluate the ending of an animal's life. It seems to matter for the animal whether it experiences pain or pleasure, or enjoyment or suffering. But does it also matter for the animal whether it lives or dies? Is a longer life better for an animal than a shorter life? If so, under what conditions is this so, and why is this the case? Is it better for an animal to live rather than never to be bo...