Mammoth or Standard donkey jacks are crossed with all breeds of saddle horses, from appaloosas and quarter horses to thoroughbreds and warmbloods. Gaited mules are extremely popular, with the mules retaining the specialized gaits of their Tennessee walking horse, Paso Fino or fox-trotting dams. Other quality bred and top performing saddle mules are used for reining, team penning, English and western pleasure. Although mules are sterile, due to the difference in number of chromosomes between a horse and a donkey, male mules need to be gelded and female mules will go through their estrus cycle and can show signs of heat. Another unique hybrid trait is heterosis, or hybrid vigor.
Mules tend to be healthier, heartier and longer-lived than horses.
They endure heat and weight better than a horse, and can subsist on poorer quality or less feed. Often their tough feet never need shoeing.