During the summer ours free range and receive some wheat and corn too.
In the winter, here in Ohio, you need to introduce some protein because there is little to be found on the yard full of ice and snow.
If you don't want commercial feed then mixing things like alfalfa, clover corn wheat can be mixed. Alfalfa leaves can be in the 30 to 38% protein range. Meat scraps are also use by many homesteaders.
If you look at the pearson's square calculator (one of our free apps) it will give you some average minimum protein levels which you can use to calculate the proteins in a rations. We show some of the proteins on the low side like wheat which is usually a little higher then 12%.
If you are determined to mix yourself -- the more diversity in the diet the better. That is, a little bit of lot of things in better than 100% of one thing.
There are production farmers that use corn or wheat, roasted soybeans, limestone, with the additions of minerals to make their own layer rations.