Horses communicate through sounds like nickering and use their manes to keep their necks warm and dry. A horse's first reaction to a threat is to flee but they may stand their ground and defend themselves. The key physical difference between male and female horses is that mares have an udder between their hind legs while stallions do not. Horses were first domesticated 4,000-5,000 years ago and live in herds, satisfying in open grasslands where they forage for food like grass and plants.