A horse donkey Cross is known as a mule. Horse donkey crosses are common and have been for hundreds of years. Mules, or horse donkey crosses, are used in any situation a horse might be. Horse donkey crosses / mules are exceptionally sure footed — often more so than most horses. Mules, however, can be more difficult to train than the average horse. Horse donkey crosses are an inter species cross, and therefore one horse donkey cross can not breed and produce offspring with another horse donkey cross. All horse donkey crosses, aka mules, are infertile. If you are interested in a horse donkey cross, you should search for more information about the animal known as a mule.