Pet donkey re-united with her owner

There was always a donkey on my grandparents farms. The one on Mum's parents place was called Brenda! The one on Dad's home farm was Jocksa. We were always jumping on them hoping to gallop round the field but they just stood there. I think they thought we were annoying little twerps!

Maybe they were stubborn donkeys. 
(Probably were annoyed by children who wanted a ride)
I remember, when I was a child, hearing the expression
"stubborn as a mule". 

I once read that a mule is the offspring of a male donkey and a female horse.
I imagine a dominant stubborn gene from both the donkey and the female horse
affected the personality. 
Or the mule was crabby about the fact that he could never have children.