I googled 'Grassado's horse' and came up with Lou Alfano's homepage.
There, there was mention of Alfana, Gradassos mare.
I'm sure there must be a more direct way to find such arcane info.
Thank you once again, Rollo, Leo-Bloom and atsgran. I tried Googling but my word order or something else only delivered detailed info on Orlando Furioso stanza by stanza. I shall try harder next time.