If I recall correctly, corn runs around 6% protein. During the winter it is ok to feed straight corn as the deer will eat it if they have no other food source. Just if all they eat is corn they will have problems. It is better to feed corn then to have them starve but don't offer corn to them when there is other feed available in the wild. Basicly, feed them when then need help and let them find their own food when the snow is gone. The one good thing about corn is that it does build the deers fat layer up so that they can handle the cold better, but like humans, getting too fat is unhealthy.
There was another deer farmer, he was Amish and fed straight corn to his animals. We advised him against this but he didn't listen. His buck as a two year old had a yealings sized rack and was over 300 pounds. Pure fat. The buck got no nutrition out of the corn and died as a 2 year old. The farmer has since switched over to the same feed we feed which is based off of Penn States formula. Our feed is custom mixed and cost around $11 per 100lbs. It is a 18% protein mixture with all the trace minerals the deer need as well as corn for Carbohydrates. The majority of the pellets is alfalfa but having all the nutrition in it helps the deer get what they need and fill them at the same time.