I don't see any nail holes. If a shoe it would have to be for a very small pony, and it would have to be nailed on. If you can find nail holes
please post more photos.
Or soak it in apple cider vinegar for 5 months - I just pulled 2 out and an ax head, hit them with a garden hose and ALL of the rust was gone - it was down to bare metal, I was pretty impressed, nail holes were cleared as well.