For thousands of years, and in almost all parts of the world people have used horses for riding, to pull heavy loads and for sport and leisure. Herds of wild horses still survive in some parts of the world-though all but the zebras of Africa are very rare. Horses ‘anatomy enables them to make use of speed to escape predators and they have a well- developed sense of balance and a strong fight-or-flight response. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and lying down....