I've spoken with animals in the underworld many times (actually, that almost seems like the point in going). Perhaps you could bring your pony along with you. That way you and your pony would be able to communicate in the different realm.
I use a pretty straight forward version of Harner's Core Shamanism (with an overlay of Brythonic Celt) to reach the underworld. I'm new here so I haven't explored the spells and articles to any extent, so there may be a description of the technique. Otherwise, I would recommend reading Harner's works...he describes it much better than I can.