Hmm, we routinely "shut down" beings that we are pretty sure are conscious, if not very intelligent. Been to McDonald lately?
Eating meat is not necessarily as ethically unproblematic as most of us would like. Ethical objections to consuming animals go back as far as Pythagoras in the West, and possibly much further in the East. The arguments for minimizing, if not eliminating, meat consumption have not gotten weaker with time. If anything, the biological discoveries showing the profound similarities between humans and other animals provide a great of justification for ethical vegetarianism.
Furthermore, we usually don't treat all animals alike. More intelligent animals, like the great apes, dolphins, and elephants, tend to garner much more respect. Should such a creature through a fluke gain human-level intelligence, I don't think the ethical implications are at all obscure; we should treat them with the same respect we give to other humans. We would at least have to set out guidelines as to how intelligent or sentient an artificial consciousness would have to be to deserve better treatment.