Hello, that guy speaking.
I thought you were just making an absurd joke, but apparently you wanted to present your remark as a valid argument in an ethical discussion. Well, in that case, you don't want to make an ethical argument from the side of the dog, do you? It might be surprising, but dogs have a severe lack of ethical understanding (or any measurable form of comprehension at all). And that leads me to say that from a *human* point of view, an animal (such as a dog) cannot possibly consent and therefore if a human(!) initiates or coerces an animal into a sexual act, it is by definition abuse.