For sure, winter here means a big jump in caloric intake. It shows in feed consumption. This is the flip side of the "no heating in the winter" conversation. The heat the chicken must produce for warmth need to come from somewhere. Our ground, as of yesterday, is also now covered with a foot...
You could, but the chances are that the Purina is very likely 70% corn already. There's not much to be gained by adding more corn beside lowering the protein and calcium your flock would be receiving. To provide some added energy and something different to pick at? Sure, why not. Be sure...