Horses are very social animals, and their behavior is what keeps the herd together and maintains the ranking of each member. It is by instinct that horses form strong friendships with other members of the herd. Mares will pair off with particular other mares, and engage in mutual grooming, which involves standing next to each other and scratching the other's neck and back with her teeth.

Horses, like other animals living in groups, are quick to establish a chain of command which lowers the number of fights over food, water, and other horses. Communicating with each other through social signals like pinned-back ears or bared teeth, the social hierarchy is soon established and a lower-ranking horse almost always gives way to a higher-ranking horse without a fight. Unlike creatures who communicate through many different sounds, the horse's number of different vocalizations is actually quite limited compared to other animals.

Wild herds consist of a stallion and his band of mares. The stallion is the top authority, who locates open places to graze for his herd, finds water, and chooses where to go. Second in command is the lead mare (where our site name comes from), who keeps the members of the herd under control, or takes over as the head when the stallion goes off on his own. She is the smartest mare, the one that all the other horses respect.

The lead mare takes care of the occasional disputes and quarrels between members of the herd. For example, if a young horse is bothering one of the mares, the lead mare will even drive him away from the herd if the problem becomes serious. This is considered a very harsh punishment because predators are far more likely to go after a lone horse than a herd. The mare is very strong and dominant, yet wise. She answers only to the head stallion, who entrusts her with the responsibility of keeping the herd together.

A horse's bonding instinct and pecking order is in a sense exploited when humans establish relationships with horses. It has been observed that many trainers will start a horse's training in the spring when horses shed and appreciate being groomed. Playing on the way bonds are established in the wild, grooming makes the horse willing to allow the human to invade his personal space and helps the two bond. If the trainer can establish a position as the top-ranking member of the herd, the horse will most likely cooperate with little or no physical force or punishment.

— AE