Horse breeding
One hypothesis held that horse populations north of Mexico originated in the mid-1500s with the expeditions of Narváez, de Soto or Coronado, but it has been refuted. Horse breeding in sufficient numbers to establish a self-sustaining population developed in what today is the southwestern United States starting in 1598 when Juan de Oñate founded Santa Fe de Nuevo México. From 75 horses in his original expedition, he expanded his herd to 800, and from there the horse population increased rapidly.