An animal’s “behavior” is the product of its genetic composition, the environment in which the animal functions, and the animal’s experience (particularly in the pre- and postnatal environment through the primary socialization period). This section focuses primarily on the diagnosis and treatment of abnormal behavior of domestic animals. For each species, normal social behavior is outlined, followed by a description of common behavioral disorders.
Horses are social animals that under feral conditions (or on pasture) live in bands (harems) that consist of several mares, their offspring up to 2–3 yr of age, and at least 1 and as many as 6 adult males. The core of the group is the mares, which stay together even if the stallion leaves or dies. The group size ranges from 2 to 21 horses; multiple-male bands are larger than single-male bands. Groups are not limited to a specific geographic area and will travel in search of resources. Colts and fillies leave the group usually before 2 yr of age (when they become sexually mature), stay alone for a few months, and then join a different group or establish a new one. Some colts may form a “bachelor band” with up to 16 males, and later join other groups in which the stallion has died or been chased away.