Mules and hinnies are hybrid offspring of donkeys (Equus asinus) and horses (Equus caballus). Little scientific information is known regarding mules and even less is known about hinnies, the reciprocal cross. Conformation standards are in place for horses but currently are not available for equid hybrids or donkeys. Conformation maybe related to functionality and longevity of equids. All animals in this study were of similar genetics (Zamora Leones and Mirandes donkey breeds and Spanish horses) from Toro, Spain and Miranda do Douro, Portugal and used for traction.