none. there is absolutely no reason to eat pork but not dog, for example, or beef but not horse. endangered animals are an exception, though i guess that's not really what the OP was asking.
i'm an ex-vegetarian, and taking a step back from the entire culture of meat-eating shows you how hypocritical it all is. now that i'm back on eating meat, i've made my decision that i'm okay fuelling my body with dead animals, and as such the only reason not to eat dog or whatever would be that i'm unconvinced by the flavour. if someone i trust tells me it's great? why not.