All the versions of Stewball, Skewbald, etc., are about (If I recall) an American horse brought to Ireland. The song exists as a broadside ballad in Ireland ("Plains of Kildare," "Stewball," etc.) and as a work song among Americans, especially black prisoners in the southern states.

"Jackson and Jane" is about an Irish racehorse, but I don't know the facts of the story.

Molly and Tenbrooks is about a real (American) horse race as well, with the real horse's name being Ten Broek.

I'm sure there are more...