Origin and significance of E-I-E-I-O in the Old MacDonald song

Question

The well-known children's song "Old MacDonald had a Farm" has lyrics in the following format:

Old MacDonald had a farm
E-I-E-I-O !
And on that farm he had {article} {singular or plural creatures}
E-I-E-I-O !
With a {creature-appropriate sound} {creature-appropriate sound} here
And a {creature-appropriate sound} {creature-appropriate sound} there
Here a {creature-appropriate sound}, there a {creature-appropriate sound}
Everywhere a {creature-appropriate sound} {creature-appropriate sound}
Old MacDonald had a farm
E-I-E-I-O !

where:

• {article} is "a" or "some"
• {singular or plural creatures} is any farmyard animal or bird, such as dog, duck, hen, cat, cow, etc.
• {creature-appropriate sound} is the sound associated with the farmyard animal in question, such as woof, quack, cluck, meow, moo, etc. respectively

So the song would go something like the following:

Old MacDonald had a farm
E-I-E-I-O !
And on that farm he had some ducks
E-I-E-I-O !
With a quack quack here
And a quack quack there
Here a quack, there a quack
Everywhere a quack quack
Old MacDonald had a farm
E-I-E-I-O !
continue with new creature

While most of the lyrics are self-explanatory, I'm wondering about the vowel sequence E-I-E-I-O ! What is the origin and significance of this particular sequence? Why not, say, A-E-I-O-U ! instead? Is there a historical, linguistic, or semantic explanation of why the song ended up with E-I-E-I-O ! as the climax of the refrain?

Answer 1

As with any folk song, the origins of the lyrics can be a bit murky, but given transcriptions collected by folklorists in the early part of the twentieth century of this or related songs, we see that the E-I-E-I-O isn't meant to refer to the letters but is rather just a vocalization to continue the melody. An Ozarks version from 1922 has lyrics:

Old Missouri had a mule, he-hi-he-hi-ho,
And on this mule there were two ears, he-hi-he-hi-ho.
With a flip-flop here and a flip-flop there,
And here a flop and there a flop and everywhere a flip-flop
Old Missouri had a mule, he-hi-he-hi-ho.

In a related song from England, there is a shorter bit of vocalization which the transcriber notated as “ī ō” (note the macron to indicate a long sound). So the answer to why not “AEIOU” is that those aren’t actually letter names being sung but simply an abstract vocalization.