No protein supplement. We have looked at it, but the corn tested 12% protein since it froze in August. Calves have access to Alfalfa/Grass hay as well as swaths. We are not planning to do corn again.
The prairie actually tests surprisingly high in protein if you get in and pull a proper sample (the stuff they eat, rather than the litter). It has run anywhere from 8%+. As well, our cows are still in their second trimester (may/june calves) and have not had calves on them for 2 months. We have thought about using DDG's as a protein supplement, but the added cost has not been justifiable when we look at cow body condition.
The swaths generally run from 8 to 12% protein depending on when it is cuts (soft dough stage). We will occasionally feed a bale or two of alfalfa/grass hay when a parcel of swaths are done to help cows clean up right to the ground.