I apologise in advance, but indeed I do find this analogy extremely poor. The main question about abortion, from my point of view, is whether what is inside the woman is a human or not. If it is, then it cannot be aborted due to the right to life: the first human right adopted by almost every nation. If it is not, analogously, it can be aborted.
So, the morals when it comes to humans and the rest of the animals are totally different. Not because we are humans and the rest “non-rational” animals are different, but because the legal frameworks are distinct. These legal norms imply drastic differences when it comes to morals.
Hence, the analogy is not poor just because there is no consensus in the society on what is what is inside the woman, but also because the legal framework—which affects the morals—is different for non-human animals.