Zebra black and white at birth. Plains and mountain zebra foals are protected by their mothers, as well as the head stallion and the other mares in their group. Grévy's zebra foals have only their mother as a regular protector, since, as noted above, Grévy's zebra groups often disband after a few months. Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. While occasionally successful, most of these attempts failed due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between
Plains zebra and not endangered, though some populations such as in Tanzania have declined sharply. A dispute exists among biologists as to how to properly classify the various species of zebras. The plains zebra and mountain zebra are thought to belong to the subgenus "Hippotigris" and that Grévy's zebra is the sole species of subgenus "Dolichohippus". This is on account of Grévy's zebra resembling an ass (subgenus "Asinus"), while the plains zebra and mountain zebra are more horse-like. All three animals belong to the genus "Equus" along with other living equids. However, recent phylogenetic evidence finds that plains zebras are more closely