The mastín Español or Spanish mastiff, is a giant breed of dog from in Spain, originally bred to be a guard dog whose specialized purpose is to be a livestock guardian dog protecting flocks and/or herds from wolves and other predators. The breed is quite alert and food motivated but can bore easily; training must be consistent and firm but gentle. Once the trainer has established the dog's respect as leader, the Spanish mastiff will be an extremely loyal pet. 3 Temperament. In medieval times, it has accompanied the herds of sheep crossing from northern to southern Spain, defending cattle from attack by wolves and other predators. 3 Temperament. In medieval times, it has accompanied the herds of sheep crossing from northern to southern Spain, defending cattle from attack by wolves and other predators. The mastiff had the protection of chunky metal necklaces with skewers. Its function was primarily protective, unlike its fellow Carea dogs, whose function is grazing, driving the herds in response to indications of the shepherd.