While I'm always pleased to see someone argue for reasons why we shouldn't kill cows, pigs or any other animal, I would challenge the assertion that they are unable to entertain hopes and dreams about the future or to remember the past with nostalgia. How would we know this? How would we know what they are thinking about? They can certainly remember the past and anticipate the future - who is to say this isn't with hope or nostalgia, and how do scientists claim to measure it's absence?