There is a recent review of Fabrizio Amerini, Aquinas on the Beginning and End of Human Life here: http://ndpr.nd.edu/news/48981-aquinas-on-the-beginning-and-end-of-human-life/. The review author states that the Catholic Church teaches that the human soul is infused at conception, and seems to imply that there is a tight connection between the Church's teaching on abortion and the rejection of delayed animation. Moreover, the author states that the debate is very heated. It seems to me that I know several Catholics who believe in delayed animation, and think that the issue has no important ethical consequences. I myself hold the second view.
I can't find any clear Catholic teaching concerning animation. Fr. Wallace and Elizabeth Anscombe (see some of the essays in Human Life, Action, and Ethics) seem to be for delayed animation. Fr. Wallace has some odd views in ethics (see his stuff on nuclear war) but Anscombe is more or less traditional.
I also can't see the direct connection between this issue and the licitness of abortion, unless maybe you knew the exact moment of animation and you thought that abortion is OK unless it is a clear case of homicide.
I have seen respectable theologians in the seventeenth-century argue that the abortion before animation might be licit in case of danger to the mother's life, but it seems to me that DS 1184 (Ann. 1679) prohibits it, although the danger seems to be from someone else and not from the foetus: ""Licet procurare abortum ante animationem foetus, ne puella deprehsa gravida occidatur aut infametur." I can't really see why it would be OK even apart from animation. It is obviously unlike a case of removing a cancer or an infected organ or limb.
At any rate, does anyone know of magisterial texts? I can't seem to find any online.