Pecking order is crucial to the social structure of the herd. When a new horse enters the band, fights ensue until the newcomer establishes a position in the hierarchy. After this initial trial, status is generally maintained by a non-violent display of threats whenever one animal comes too close to another.

Horses form cliques, and friendships, keeping company throughout the day's activities. They often engage in mutual grooming behaviors. One horse will approach another with an obvious invitation readable on its face: "Lets scratch backs." If the other horse agrees, each horse, beginning at the neck, gently nibbles and scratches her companion with her teeth, often working her way to the root of the tail. Studies have shown that this is more than a pleasant back scratch. It grooms the coat, and tends to strengthen the social bonds between horses. Zoologists Claudia Feh and Joanne Demaizers discovered that when a horse's withers are nibbled in this fashion, her heartrate slows by 10% on average. Mares typically engage in mutual grooming with their foals, the stallion grooms with his favorite mares, foals of similar ages groom each other, and friends groom friends.

And stallions do have favorite mares. Just as some gentlemen prefer blondes, some studs are attracted only to mares of a certain color. This is usually the color of his mother. Some studs will even go so far as to collect a band of mares all of the same color. Some domestic stallions will refuse to mate with mares of the "wrong" coat color. Most stallions prefer the highest ranking mares and show little interest in fillies ,under the age of three, especially if they are his own daughters. A stallion herds and harasses the lower ranking mares with far less patience than he shows with the lead mares. Like people, horses have personality conflicts. A stallion may be affectionate with one mare, and bicker constantly with another.

The stallion is the protector of the herd, and during breeding season, keeps them together in a tight band. However, it is the lead mare who usually makes the routine decisions, such as when and where the band goes for water. Even mothering skills vary from mare to mare. Some mare-foal duos are very closely bonded, seldom far from each other's sides. At rest they stand close, bodies touching. Foals from previous years also tend to stay close to their mothers, especially the fillies.