Animals have life, so they must have a soul, so what happens to them when they die? You see, every animal has a sort of life, but every animal does not have options to do good deeds and to do bad deeds, so there is no examination for them, so their souls are not preserved, moreover they are not fully developed and mature, because what is soul after all without consciousness?
You have a soul, what does it mean? You can see, you can hear, you can make your own judgments, you can love, you can hate, you can run towards something, you can be rebelled from something, you can have hope, you can have fears, all these things make a soul, so the consciousness, human consciousness is so great that it is capable of understanding superior things, like God, like the existence of spirits and so on.
Animals and poor things are at a much lower stage of development, they can’t understand beyond their limited course for which they are created, the cow doesn’t understand except to bear calves and to eat grass and to drink and to die, and small fears of course, but human beings are made for much wider understanding of the universe, as such their souls are fully developed, they are preserved because they have begun already to understand their creator and they have also been born with a desire to meet God and to know him and to love him.
These animals don’t understand these things, so there is no meaning in preserving these souls, but I don’t deny that either, maybe in some form Allah does preserve their souls but we don’t know of that, okay?