Time has a fantastic piece that looks at to what extent animals think and feel:
But one by one, the berms we’ve built between ourselves and the beasts are being washed away. Humans are the only animals that use tools, we used to say. But what about the birds and apes that we now know do as well? Humans are the only ones who are empathic and generous, then. But what about the monkeys that practice charity and the elephants that mourn their dead? Humans are the only ones who experience joy and a knowledge of the future. But what about the U.K. study just last month showing that pigs raised in comfortable environments exhibit optimism, moving expectantly toward a new sound instead of retreating warily from it? And as for humans as the only beasts with language? Kanzi himself could tell you that’s not true.
I’m coming around to the viewpoint that vegetarianism is the only morally justifiable approach.