List of leading Thoroughbred racehorses information

The list of leading Thoroughbred racehorses contains the names of undefeated racehorses and other horses that had an outstanding race record in specific categories. Note though that many champions do not appear on the list as an unexpected defeat may be caused by many factors such as injury, illness, going, racing tactics and differences in weight carried, the latter being particularly significant in North America and Australia where handicaps are common even at the highest level of racing.

It is common to compare racehorses on multiple factors such as their overall race record, the quality of the horses they beat and the brilliance of their wins. Comparison of raw times is generally unreliable between horses of different eras or even over different racecourses due to a variety of factors such as the racing surface and the pace at which the race is run. Timeform ratings, introduced in 1948,^[1] and Beyer Speed Figures, introduced in the United States in 1992, are relatively recent attempts to compensate for such variables.^[2] Thoroughbred Winning Brew holds the Guinness world record for the fastest speed from the starting gate for a Thoroughbred racehorse, at 70.76 km/h (43.97 mph) over two furlongs,^[3] although Quarter Horses attain higher speeds over shorter distances than Thoroughbreds.^[4] Such speeds may also be achieved by elite racehorses during the stretch drive.^[5]

The two main forms of Thoroughbred horseracing are flat racing and hurdle or steeplechase (jumping) races over obstacles. Jumpers tend to be older than their flat racing counterparts^[6] and can have much longer careers, making it possible to earn a large number of wins. For example, champion hurdler Hurricane Fly won a then-record 22 Grade One races over his ten-year career.^[7]

Most race horses and race winners are male horses (either intact males or geldings). While male and female horses do not exhibit sexual dimorphism as obviously as human athletes, male horses are considered more aggressive racers and generally have a significant competitive advantage. At the highest level of racing though, intact males have great economic value at stud, so they are often retired after only a few years of racing.^[8] In part because they may have longer racing careers, some of the most winning racehorses of all time are females, including Kincsem, Black Caviar, Winx, and Zenyatta.