Why does the mother animal take care of its baby?

Because they love them like our mother cares for us (unconfirmed as yet), the same way they care for their baby. The majority of animals (as yet known) will have the mother caring for its young. In cases of mammals, the female is the provider of the initial food (milk) so it becomes the main role. In the life of a sea horse the male is the caring parent rather than the female.

2nd Answerer says: It is entirely possible that the physical duress involved with a living being COMING OUT OF YOUR BODY just might instill some level of fealty.