I'm actually interested in therio as well, but not in the horse world. I have been talking with a few therio people here at the vet school to get a better idea on residencies and such. So, I'll be following this thread a bit- if anyone has any other kind of information, that would be awesome!
From what I talked to with the professors here- they said that you need to pick an area of therio (if that is large animal, horses, small animal, whatever...) If you want to do it all- pickings are very slim for those residencies.