When I was in the All-Philadelphia Boys' Choir in 1962 (I was a first soprano!) we sang a choral version of this song, with the title "Whoa, Mule, Whoa". As best I can recall, the lyrics were:

Once I had an old black mule
I found him in a holler
Tied a slipknot in his tail
His head slipped through the collar

Hurry hurry help me
Hee-haw, hee-haw, hee-haw
Hurry hurry help me
Hee-haw, hee-haw, hee-haw
Whoa mule I tell you
Whoa mule I say
I have no time to pet you now
But don't you run away...

I think there was a second verse, too, but it's long gone from my memory. At the end, the whole choir shouted "Whoa, mule, whoa! Whoa.......mule!"

I knew you'd all like to know that.

Aloha,
Mark