If you are taming an animal and it has been damaged while within range of a deer:
the animal will be healed -and- the taming indicator/number will jump 30-50 points. It goes
above 100, and appears to not change cow to domestic but bugs it out so completion cannot
happen.
I discovered this after initial 20 pts of taming, dragging a cow through pine forest. It was healed
by a random deer, so I proceeded to tag a deer, trap it at home and repeated.