Who eats oats? Posted by Jeff

Does eat oats and goats eat oats but little lambs eat ivy.
A kid'll eat ivy too, wouldn't you?

My wife contests that it should be:

Mares eat oats and does eat oats and little lambs eat ivy.

Yet another variation found on the web is:

Mares eat oats and goats eat oats but little lambs eat ivy.

I saw someone else faced with this quandry had proposed dropping the other animals entirely in lieu of giraffe.

Help? From whence should the absolute authority derive for this little rhyme?

P. S. I'm not necessarily looking for which one is older or more original, but which one is fundamentally better.