I actually thought this was a bit of a windup - but no it's not! from wiki -
"The offspring of a zebra-donkey cross is called a zonkey, zebroid, zebrass, or zedonk. zebra mule is an older term, but still used in some regions today. The foregoing terms generally refer to hybrids produced by breeding a male zebra to a female donkey. Zebra hinny, zebret and zebrinny all refer to the cross of a female zebra with a male donkey. Zebrinnies are rarer than zedonkies because female zebras in captivity are most valuable when used to produce full-blooded zebras. There are not enough female zebras breeding in captivity to spare them for hybridizing; there is no such limitation on the number of female donkeys breeding."
And some more pics
And not just donkeys... Get around these zebras...