I read the assertion in the link with some interest. I note that the terminology here is different from what I heard around the farm. But what is done with this non-sterile mule mentioned therin? Who's his baby?
Don't know. Never saw it happen myself.
Ironically, I learned that mules are not always sterile in Asimov's Foundation series --- had to go look it up, because, like you, I thought mules were always sterile.