In this book, law professors Sherry F. Colb and Michael C. Dorf argue that:
many non-human animals, at least vertebrates, are morally considerable and prima facie wrong to harm because they are sentient, i.e., conscious and capable of experiencing pains and pleasures;
most aborted human fetuses are not sentient -- their brains and nervous systems are not yet developed enough for sentience -- and so the motivating moral concern for animals doesn't apply to most abortions;
later abortions affecting sentient fetuses, while rare, raise serious moral concerns, but these abortions -- like all abortions -- invariably involve the interests and rights of the pregnant woman, which can make these abortions morally permissible.
For a book claiming to explore the "connections" between debates about the two issues, just the summary from the book flap -- basically, what's above -- makes it appear that there really isn't much connection between the topics, at least at the core ethical level. Animals are sentient, early fetuses are not, and so the moral arguments about the two issues don't overlap or share premises. While the authors hope to use insights from one issue to shed light on the other, I find that differences in the issues limit these insights.