Animal Ethics

I am not sure any moral consideration of non-human animals in relation to humans (because this is the real issue; if humans were to not use animals for any purpose, than I think it could be agreed upon that animals should be given consideration solely on the knowledge of their existence, as our species and the environment around us, including other species, does not sustain and thrive on cruelty and destruction) can be considered prior to any specific situation. As other species have become a means to human ends, and this occurs because there is no doubt that a separation exists between human species and others we have encountered (call it speciesism or whatever, that is irrelevant), when is this, if it is, permissible? And this can be evaluated on a case to case scenario; I am not sure one can correctly (or convincingly) argue flat out that it is permissible to kill or not to kill other species. I am curious as to the implications of this, and other ethical issues, as there is no black and white with some of these issues, save perhaps on a case to case basis. For instance, in the case with self-conscious non-human species, one may hold that if there are alternative, accessible and affordable, options to eating self-conscious animals (say pigs), one should take the alternative, as a self-conscious animal can take a conscious interest in its life, something humans can relate to and value perhaps more than anything. However, if there is no alternative, and the human needs to eat, is it ethically permissible to kill the self-conscious animal for food, as painless as possible?

Also, is it not these human specific traits that come up in conversation, such as moral agency, a high level of rationality, and the very ability to entertain these traits in conversation, that allow us to single out our species in relation to any other? Does this warrent some partiality? Thoughts of superiority? How is superiority determined? And can say the superiority of the cheetah with its ability to run faster than humans be outweighed by the humans superiority to be or have any of the traits noted above?