Cow observations - what they choose to eat.

I have just two Jerseys. While moving one to a new paddock, I tired her up to a tree that had a pile of maple tree branches lying next to it that I had cut a week earlier. Instead of going for the few patches of tall grass within her reach, she started eating the maple leaves off the branches. She wasn't starving by any means so I guess she liked the taste. Anyways, I'm wondering if these would be good to add to her diet cause I have lots of maple trees.

Whoops, never mind. I just read that it can be toxic to cattle. I won't be giving her anymore.