I've always heard that if an animal is stressed before it dies, the meat doesn't taste as good. But among the few wiltshire sheep that I have accidently killed poorly, who unfortunately suffered a bit before I could get them properly killed, actually tasted better than anything I've ever tasted. I'm sad to think that animals might want other animals to suffer a bit in order to ramp up the flavor... terrible thing, and not something vegans are going to want to hear.

I've also heard that older animals don't taste as good. But I've found that sheep that are about 3 years old taste the best -- not tough yet, and full of flavor. Too old and they get tough. "Lamb" (up to 1 year old) may be the most tender, but the flavour hasn't developed enough yet.