query: How fast is the fastest horse in the world?
passage: List of leading Thoroughbred racehorses
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 in different countries 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 for a Thoroughbred racehorse, at 70.76km/h (43.97mph) over two furlongs,[3] although Quarter Horses attain higher speeds over shorter distances than Thoroughbreds.[4] Looking at average speeds for longer distances may be misleading as many races are run with a slow initial pace followed by a sprint in the stretch drive.
passage: Pronghorn
The pronghorn is the fastest land mammal in the Western Hemisphere, being built for maximum predator evasion through running. The top speed is very hard to measure accurately and varies between individuals; it can run 35mph for 4mi (56km/h for 6km), 42mph for 1mi (67km/h for 1.6km), and 55mph for 0.5mi (88.5km/h for 0.8km).[16][20] It is often cited as the second-fastest land animal, second only to the cheetah.[21] It can, however, sustain high speeds longer than cheetahs.[6] University of Idaho zoologist John Byers has suggested the pronghorn evolved its running ability to escape from extinct predators such as the American cheetah, since its speed greatly exceeds that of extant North American predators.[6][22] Compared to its body size, the pronghorn has a large windpipe, heart, and lungs to allow it to take in large amounts of air when running. Additionally, pronghorn hooves have two long, cushioned, pointed toes which help absorb shock when running at high speeds.[23] They also have an extremely light bone structure and hollow hair. Pronghorns are built for speed, not for jumping. Their ranges are sometimes affected by sheep ranchers' fences. However, they can be seen going under fences, sometimes at high speed. For this reason, the Arizona Antelope Foundation and others are in the process of removing the bottom barbed wire from the fences, and/or installing a barbless bottom wire.[24]