Actually, it is only Wizards who wish to take over animals. Witches don\'t.

Wizards are just some evil people who want to ruin everything with their magics.
Witches use a much smarter technique, they call the animal, not by picking up the phone, but they use their special abilities to make it approach, where they then enter it\'s mind. There, the Witch share the animal body with the animals mind. Now for the crucial part - They don\'t abuse the animal by taking control of it, they just slightly push the it in the direction they want to go. If one is to fully take over an animal body, there should be losses. If you do it for too long, you begin to become the animal, and you forget who you are, as in you loose stats/skills. If you are to fully become the animal, someone has to pull your mind out of the animals head, or you\'re lost forever.

.... Wizards never figured a spell to take over animals so they stopped trying to do it.

Edit: Btw, I got this stuff from a book that explains everything about magic (it also explains why Gandalf doesn\'t have a wife).
