A mare carries her foal for about 11 months before giving birth. This period may vary from 10 to 14 months. Foals can stand shortly after birth, and within a few hours they are able to run about. The legs of newborn horses seem much too long for their bodies. As the horse matures, the legs grow more slowly than the rest of the body.
A year-old colt is often more than half grown. Most horses reach full height and weight by the age of 5. Most horse raisers start to breed mares at the age of 3 or 4. They start to breed stallions at the age of 4. Most mares have five or six foals during their life, but some have as many as 19.