Horses And Ponies, Stallions And Horses, Stallions And Mares

Stallions will 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 aggressive behavior, particularly toward other stallions, and thus require careful management by knowledgeable handlers. However, with proper training and management, stallions are effective equine athletes at the highest levels of many disciplines, including horse racing, horse shows, and international Olympic competition.

Contrary to popular myth, the stallion is not the leader of a herd, but defends and protects the herd from predators and other stallions. The leadership role is held by a mare, known colloquially as the "lead mare" or "boss mare." The mare determines the movement of the herd as it travels to obtain food, water, and shelter. She also determines the route the herd takes when fleeing from danger.

When the herd is in motion, the stallion brings up the rear, keeping straggling herd members closer to the group and serving as a "rear guard" between the herd and a potential source of danger. When the herd is at rest, all members share the responsibility of keeping watch for danger. The stallion usually is on the edge of the group, to defend the herd if needed.

In a herd or a group of horses, there is usually one mature herd stallion. Both sexes of horses are tolerated while young, but once they become sexually mature, the stallion will drive both colts and fillies from the herd. Colts may present competition for the stallion, but studies suggest that driving off young horses of both sexes may also be an instinctive behavior that minimizes the risk of inbreeding within the herd. In some cases, a single younger mature male may be tolerated on the fringes of the herd. One theory is that this young male is considered a potential successor, as in time the younger stallion will eventually drive out the older herd stallion.

Fillies usually soon join a different band, but colts or young stallions without mares of their own usually form "bachelor bands" in the wild. Living in a group gives these stallions the social and protective benefits of living in a herd. A bachelor herd may also contain older stallions who have lost their herd in a challenge.[

Other stallions may directly challenge a herd stallion, or may simply attempt to "steal" mares and form a new smaller herd. In either case, if the two stallions meet there rarely is a true fight; more often there will be bluffing behavior and the weaker horse will back off. Even if a fight for dominance occurs, rarely do opponents hurt each other in the wild because the weaker combatant has a chance to flee. Fights between stallions in captivity may result in serious injuries; fences and other forms of confinement make it more difficult for the losing animal to safely escape. In the wild, feral stallions have been known to steal or mate with domesticated mares.