In June, veterinarians at the Prague Zoo administered a check-up to Cassovia, a 550-pound female Przewalski's horse, before moving her to a new home on the Asian steppe. Natives of Mongolia, China, Russia and Eastern Europe, Przewalski's (pronounced "shah-val-ski") horses are the last wild horses left on Earth. Unlike the feral horse population of North America, the species has no domestic ancestors. Hunters and environmental pressures all but wiped out the animals by the 1970s, but about 1,500 remain in captivity. Conservation organizations have reintroduced another 400 into preserves in the steppe.