wow holly, I've never seen a mule mane that long. I've seen like 6" long. As far as breeding goes, I would not use a mammoth jack. I would find a large standard instead. It's not unusual for a mule to surpass the height of it's parents, and unless you found a more elegant mammoth jack, I'm afraid that the movement you are looking for wouldn't be there. However, I'm sure if you looked hard enough, you could find a mammoth that would work. As far as I know, people tend to use the large standards for more refine saddle mules, rather than draft mules out of mammoth jackstock.