Ouch!!
If your getting rid of livestock maybe you have a couple castration bands you can introduce your friend to
I would say start at 220 - 300 grit and work your way up. You probably wont get all those marks out but at least he didn't chip the edge. It may or may not be pretty but it should still shave really well when your done.
Theres a Hand Sanding howto here somewhere, if you search you should find it
Bob