A stallion is a male horse that has not been gelded. Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, cresty neck, as well as a somewhat more muscular physique as compared to female horses, known as mares, and castrated males, called geldings. Temperament varies widely based on genetics, and training, but because of their instincts as herd animals, they may be prone to aggressiv