<P> 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 Kentucky Derby, the Preakness Stakes, the Belmont Stakes, the Melbourne Cup and the Breeders' Cup Classic . </P> <P> 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). </P> <P> Until the invention of castration and even later where there was less cultural acceptance of the practice, mares were less difficult to manage than stallions and thus preferred for most ordinary work . Historically, the Bedouin nomads of the Arabian peninsula preferred mares on their raids, because stallions would nicker to the opposing camps' horses, whereas mares would be quiet . However, other cultures preferred male horses over mares either due to a desire for more aggressive behavior in a fighting animal, or to not be inconvenienced with a loss of work ability due to a mare's pregnancy, parturition and lactation . </P> <P> The word mare, meaning "female horse", took several forms before A.D. 900 . In Old English the form was mere or mȳre, the feminine forms for mearh (horse). The Old German form of the word was Mähre . Similarly, in Irish and Gaelic, the word was marc, in Welsh, march, in Cornish "margh", and in Breton marc'h . The word is "said to be of Gaulish origin ." The word has no known cognates beyond Germanic and Celtic . One possible derived term is a mare's nest, an expression for "excitement over something which does not exist" The term nightmare, is not directly connected etymologically with the word for female horse, but rather to homophones that meant "incubus" or "goblin ." </P>

When does a filly first come in season