What is sent to Gargantua in Gargantua: Chapter Fifteen? What does he do with the gift?

Grangousier receives a gift from another king, which is the gift of a giant mare that is as big as six elephants, has a horn on its hind quarters, and has a tale as big as a pillar. Grangousier deems such a beast as the perfect horse for Gargantua to ride to Paris.