I think I may have written about this in a blog entry or at least a response on the board. Animals choose their lives knowing it's a possibility (perhaps even a strong one) that they are going to be slaughtered. Why? To serve as an example; to provide yet another opportunity for people to wake up to their compassion.
Animals don't seek revenge on humans once they are dead as far as I'm aware. I've never encountered an angry cow/steak in the afterlife.
