Thanks for the comments all!
Kilroy, my mature bulls winter on alfalfa/clover/grass mix hay. If the hay is lacking or we hit a really rough stretch of weather, I will throw out some baleage, or even a lick tub. If my big guys can't maintain condition in this set-up, they take a ride. The younger bulls get a high protein ration, with less fat than most push, and access to the same hay as the mature bulls. I do not use a TMR and do not feed DDG to anything. The exact ration changes based on what is economical. This year, corn is cheap, and big rounds are going for as cheap as $10 a bale (probably not greatest quality for sure), so I will have to figure that into the equation. I don't like to push them with too much corn, since it gets them too greasy and has negative impact on semen quality, but at the price they are forecasting, I will have to make use of some corn.