On horses, the mane is the hair that grows from the top of the neck of a horse or other equine, reaching from the poll to the withers, and includes the forelock or foretop. It is thicker and coarser than the rest of the horse's coat, and naturally grows to roughly cover the neck. Heredity plays a role, giving some horses a longer, thicker mane, and others a shorter, thinner one.

Source: Wikipedia