Then why is it wrong for a human to kill another human, but it's okay for us to kill and devour a cow?

(I am in no way a vegetarian or vegan. I'm just using that example as an argument.)

Also, if those creatures have souls as well, then why are they incapable of logic or reasoning? Why are they incapable of collective advancement? And most importantly, why are even the most advanced of animals only capable of an infantile level of communication with human beings or with their own species?