A horse is a horse, of course, of course...
Horses are lively and high-spirited. They are happy in fields, can smell war, are provoked to race by a voice, are called to battle by the sound of the trumpet, grieve when defeated and exult when victorious. Some horses can recognize an enemy in battle and attack by biting. Some recognize only their masters and will allow no other to ride them. Only the horse weeps and grieves for its dead or dying master. Mares are sometimes impregnated by the west wind. There are three kinds of horses: noble, good for battle and work; common, good for carrying burdens but not for riding; and hybrids, born from a mixture of two kinds.
Most sources have a long chapter on horses, which includes not only the attributes of the horse, but also examples of famous horses and tips on what makes a good horse.