I knew that they would interbreed but I remember hearing at a summer show an "expert" stated that while it is true that a mulie buck will breed a whitetail doe, the converse is the norm: whitetail buck/mulie doe. He opined that it was because whitetail bucks are more aggressive breeders.

Regardless, do you think that the offspring are always sterile? This is what I've heard.

Yesterday I witnessed something I've never seen. I sneaked up to a vantage point and right below me at about 150 yds. was a Muley buck with a Whitetail doe. After they finished their business, this doe and another Whitetail doe started fighting with their front feet. I watched them for over an hour.