Jody, I have seen cattle wintered on grass that do well and I have seen cattle wintered on grass that are thin to the point of even being 'poor.' There is a difference. It all depends on the owner of the cattle and how he supplements them. You can be a low-cost producer, but where people get into trouble is being a NO-COST producer. It just won't work. Some get away with it for awhile, until, like one place I know, they had 70% open cows. In some situations cows don't last in the herd very long. One just needs to know the whole story.
A lot depends on when you calve. If you winter 'out' those producers usually calve later.
We have a customer that is a great stockman. He feeds his own alfalfa hay to his cows. 10# every other day when he has grass to graze. He watches a lot of things. How the manure is stacking; if they are laying down around noon (shows they are getting enough to eat;) whether they are all grazing the same direction (shows they are competing for grass). He OBSERVES his cattle. He does feed them hay when they tell him he needs to. This producer gets 85% bred in the first heat cycle; end of March calves weigh 630# first week of October. He buys no supplement except mineral. In this cold weather he has been feeding 35# grass hay. He doesn't go by the calendar, he goes by what the cows dictate. He said if he were to feed cake, he would feed 5# of wheat midd pellets. He makes sure the cows have all the water they need. Water is so important. I don't understand how people like Kit Pharo say that cattle can winter on hay. I wonder how long those cows stay in the herd.
Water is the first required nutrient.
Then we know of a fellow that is strictly grass and cake; his cows always look good. He has great winter protection. So it can be done, but like this winter, it can't be done very cheap.