Animals are as much aware of their existance as we are of ours. They have the same spirit as humans. They experience emotions, which is quite evident from dogs, who are happy when their owner returns home, and know they have done bad when the shit on the carpet, and cower in fear when you go to rub their nose in it.
I think that if animals ever were immortal like humans were supposed to be, the reason they are not now is because that if they remained immortal and humans were cursed, then eventually humans would find the secret to why the animals dont age and die through genetics and fix humans. And then the evil "elite" people will live disease free lives not aging or dying and all the rest of the population would die out.