mn-
Your question might be a quick one, but the answer(s) are NOT quick! Nutrition of beef cattle is as important as optimal genetics, and especially in the part of the North American Continent in which you are located! Your winters can be brutal at times, and the humidity doesn't help in allowing a cow to maintain her own body heat. That requires NUTRITION, and adequate and correctly balanced amounts. Along with the grass hay, alfalfa bales and some corn stalks, you would be well advised to have a complete mineral supplement available free choice, and to have your current feedstuffs chemically analyzed so as to KNOW what is going into your cattle - not just THINK that you are covering all of their needs!
Following are two web sites which I recommend HIGHLY for your perusal to find the answer to your question. They both go into clear detail, which will provide you with information and enable you to KNOW that your nutritional needs are satisfied, and your cows will survive the winter in great condition. And their calves will make you money next year!
Access these two sites, copy the work, do what they suggest, and RELAX!
www.extension.umn.edu/Beef/components/publications
ohioline.osu.edu/as-fact/0001.html
DOC HARRIS
ps- I just tried to get this information, and it didn't work! Go to "DOGPILE", type in the box "Winter Nutrition for Beef Cows" (without the quotes) and look for this title: Beef Cattle Management Update. CLICK on it.