growing, usually by age four or five. A healthy, well-managed mare can produce a foal every year into her twenties, though not all breeders will breed a mare every year. In addition, many mares are kept for riding and so are not bred annually, as a mare in late pregnancy or nursing a foal is not able to perform at as athletic a standard as one who is neither pregnant nor lactating. In addition, some mares become anxious when separated from their foals, even temporarily, and thus are difficult to manage under saddle until their foals are weaned. The formation of the bond between a mare and her foal "occurs during the first few hours post-partum , but that of the foal to the mare takes place over a period of days". Behavior Mares are considered easier to handle than stallions. In wild herds, a "boss mare" or "lead mare" leads the band to grazing, to water, and away from danger. She eats and drinks first, decides when the herd will move and to where. The herd stallion usually brings up the rear and acts as a defender of the herd against predators and other stallions. Uses Mares are used in every equestrian sport and usually compete equally with stallions and geldings in most events, though some competitions may offer classes open only to one sex of horse or another, particularly in breeding or "in-hand" conformation classes. In horse racing, mares and fillies have their own races and only a small percentage compete against male horses. However, a few fillies and mares have won classic horse races against colts, including the Prix de l'Arc de Triomphe, the Kentucky Derby, the Preakness Stakes, the Belmont Stakes, the Melbourne Cup and the Breeders' Cup Classic. Mares are used as dairy animals in some cultures, especially by the nomads and formerly nomadic peoples of Central Asia. Fermented mare's milk, known as kumis, is the national drink of Kyrgyzstan. Some mares, usually of draft horse breeding, are kept in North America for the production of their urine. Pregnant mares' urine is the source of the active ingredient in the hormonal drug Premarin (derived from Pregnant mares' urine). Until the invention of castration, and even later where there was less cultural acceptance of castration, mares were less difficult to manage than stallions and thus preferred for most ordinary work. Historically, the Bedouin nomads of the