Namib Desert
Due to scarcity of water, the Namib Desert horse sometimes goes without water for as long as thirty hours in summer and has been known to go close to 72 hours without water during the winter, significantly longer than most horses, even other feral herds. A 1991 study suggested that in 75 years of genetic isolation and water scarcity the population had developed physiological mechanisms which improved their ability to conserve water. In 1993, a second study showed that the physiological water-conservation ability did not differ between Namib Desert horses and other populations when dehydrated for periods of up to 60 hours, but suggested that the Namib Desert horse would show improved conservation ability when dehydration periods were extended to upwards of 72 hours, a common occurrence in their feral state.