We don't run them on stalks to often but my first year with cows we did and we didn't do anything to fill them up.. I'm thinking we probably got lucky but we ran them on 125 acres of corn along with 25 or so acres of Millet that we had planted in a failed alfalfa strip... Most folks I know just turn them out into the fields in the afternoon after filling them up a bit..
That being said as I have been baling the stalks in some crop ground this year I don't think I would want to turn cows out on it with no protection as there is tons of corn on the ground in those fields... Something with the way that this farmer does things leaves giant piles in the field where they load. I think they are going to fast or something, who knows.... Also, a lot of corn stalk rot this year meant a lot of down corn, those fields would be a nightmare too..
Have lost one bull from corn founder right about when 9/11 happened (Remembered because I had to go to the store to get medicine and almost ran out of gas because we had 3.00 gas that day and I refused to pay it.) He got into a grain auger during the day they were moving corn so the area was just full of grain... He ate tons of it.. Was very sad and I kicked myself but I still don't know how that gate got open.