Northwestern Study Abroad

I’m looking at Northwestern and want to study abroad, but have found that they don’t offer anything I’m really interested in, so I’m wondering how easy is it to go third-party with Northwestern? I’ve seen some programs I really like that are offered by Columbia and Berkeley, and want to know if I can go on them without attending those universities. And also, how strong is Northwestern with prereqs such as like animal science, wildlife bio, general bio, etc? Thanks!

Many, perhaps most, of these study-abroad programs would be open to outside students:

http://www.bestcollegereviews.org/best-study-abroad-programs/