Ertz (2008-10, p.764) lists a copy attributed to Frederick van Valckenborch in a private collection, copper, 27.5 x 37, illustrated in Múllenmeister 1978, vol.3, nr. 464. This seems extremely unlikely to me.
The horse in this painting is awkwardly sized somehow. It shows how Jan is struggling to find some formula to heroize the horse, which had not been a very strong animal in his early paradise landscapes but would become one with help from Rubens's studies later on. In this one I think he's looking at drawings he might have done of Titian's Adoration of the Magi from Borromeo's collection.