On the racing mules issue...yes, they are out of thoroughbred mares, at least the ones here(NM) are. A member of our Rio Grande Mule and Donkey Club has the current "fastest mule" in the country. He brought some of the race videos to a meeting for us to see. We thought it was sort of funny that some mules take a scenic tour down the track so it helps if the mule runs straight! He races them in CA. I hear they used to race here at our State Fair years ago but didn't get enough competitors.
StarWish/Colleen