http://en.wikipedia.org/wiki/Donkey
More fun farming facts, this time linguistic rather than biological in nature:
The word donkey (and its equivalent, ass) is one of the most etymologically obscure in the English language. Until quite recent times, the standard word was ass, which has clear cognates in most other Indo-European languages. No credible cognate for donkey has yet been identified, though it is possible that it is a diminutive of dun (dull greyish-brown), a typical donkey colour; and originally, “donkey” was pronounced to rhyme with monkey.
In the late 18th century, the word donkey started to replace ass, almost certainly to avoid confusion with the word arse, which, due to sound changes that had affected the language, had come to be pronounced the same way. The US pronunciation of ass was eventually restored to /