Rather than one set of ethics which applies to Homo Sapiens and another which applies to all other species, we need to need to have one set which applies to all species, with consideration for their level of sentience. The idea that all people are equal (and all other animals lesser) is a legal concept necessary for a crude democracy to function. We need better means to judge an entity's level of sentience or "humanness". Conflicts between animal users and animal rights activists often result from the lack of such an ethic.
I believe it's naive to support the welfare of others (such as animals) with no recognised intention of profit of any kind for oneself. There is no such thing as pure altruism. Each entity, including each species, nation, organization etc., ultimately works for what it sees as being in its own best interest. "Humans" are different in that they have a value system. What's good for my value system is psychically good for me. If I work for the survival of an animal, it's because I respect that animal's sentience, or its spirit if you like. Therefore I'm working for my own value system. If I don't gain materially from an act, at least my set of moral principles is satisfied. As a necessary part of civilization, most of us are programmed to get pleasure from the pleasure and comfort of others. But one way or another, it's all about "my" pleasure and comfort.
It's argued that there are reasons beyond the practical, beyond even the effect on the human psyche, which demand humane treatment of animals. There are reasons of self-respect and good conscience, but these are still practical, human oriented reasons. It not enough to say that causing pain is wrong because it hurts. I don't suffer the pain I may cause in another animal. I may suffer the guilt of having caused it unnecessarily. Fear, pain and the guilt of having caused it, detract from our ability to communicate. The guilt, or bad conscience, are only subconscious recognition of this fact.
When I kill an animal, it may be a crime against that species (a hunter killing the biggest, healthiest deer), against the universe (killing an entity of relatively high sentience), or eventually against my species and myself (killing too many to maintain the herd). But the only possible crime against the animal itself is the suffering of pain of fear which I may cause. Yes, I know that it would be difficult to kill an animal without at least a moment of pain, but this must be compared to the ways that it might die naturally. I must add also that my ability to recognize an entity's suffering is proportional to the similarity between its means of communication and mine. Once an animal is dead, it represents a level of sentience no higher than that of complex organic compounds. What happens to it then can not be of great moral significance.
If I torture an animal to death, the main ongoing effect it will have is on my own psyche. Suppose then that I am expecting to die soon afterwards. Is there a significant moral reason for opposing torture in this case? I think it's only in the guilt I, or a spectator, might suffer in the interval. My background has programmed me to dislike such activity, or the knowledge of it's being performed by others. Again, this is a self-centered reason.
The argument is made that by domesticating animals, we don't allow them to evolve naturally. In the simple version, this isn't precisely correct. Wild strains are usually still free to evolve. But we do reduce their number, often critically, often by destroying their habitat to make room for our domesticated strains. (The excellent book Ishmael expresses this thoroughly.) But does that mean that symbiosis is bad? A symbiotic pair such as lichens (algae and fungus) ants and aphids or humans and cows, evolve together as one species, each somewhat controlling the evolution of the other.
Some people might point out that animals have been using other species as they see fit since the beginning of life on earth, with very little concern for their suffering. In fact house cats, which many of us value as gentle pets, can be quite brutal. The human race gained its place in the world by the most basic law that animals live by, survival of the fittest. (Of course "fit" is open to interpretation, but ultimately, the one that survives is fit, therefore able to continue evolving to something better.) But technology gave us so much superiority, to quickly for other species to evlove defenses, that we're no longer forced to kill only the sickest and weakest. But hopefully enough of us are also moving beyond the simple ethics of lower animals. Will we one day get smart enough to go back to actually culling, so that all species can evolve together? It's certainly in our best interest.
There is a continuum of levels of sentience, including the smallest, simplest one-celled organisms to humans, with many overlaps between species. An animal may have a similar physiology to that of humans and is therefore a technologically valid subject for medical exeriments. This doesn't mean that it necessarily has similar mentality or capacity to experience suffering, or that we must give it equal rights with humans (the direction taken by some eastern religions). In my mind, the level of sentience corresponds pretty well to the order of evolution, the complexity of the nervous system (indicated partly by the complexity of its actions), and therefore to its ability to suffer and enjoy.
On one hand we have non-Homo Sapien primates, dolphins, wolves etc., some of whom have the potential for "talking". All have some degree of sentience, awareness and value in the developing universal sentience, and are somewhat able to communicate their sentience to us. On the other hand, we have hospitals for the purpose of maintaining idiot Homo Sapiens, human only in body, who have barely enough mentality to keep their organs functioning. They have never learned, and will never learn, coordinated movement or communication. We maintain their bodies by the thousands until they die of "natural causes". Which are more human? Which are more morally appropriate for medical experiments? Should species, or sentience, be the criteria? I think it depends on which we can feel most in community with.
Should we consider breeding idiot lower animals, that won't mind small cages etc., for food production (probably not economical)? To extend this further, would it be morally valid to breed a strain of idiot Homo Sapiens for medical experiments, organ transplants etc.
Some primates have shown a reasonable intelligence and ability to communicate with us. Shouldn't they therefore have the same rights to free education, health care and taking part in human society as do non-speaking, retarded Homo Sapien children? I might feel more sorry for them after than before.
Once in a zoo I leaned over the railing and stuck my finger through the wire of a monkey cage. A monkey came over and held onto my finger for a moment and then went away. We were in effect shaking hands. I was saying that I cared about him and trusted him, and I think he understood. It's seldom I have a chance to feel more intimate or have more meaningful communication with a human - a sad commentary on human relations.