I have a bunch of chickens that are penned all the time and others that get come degree of free-range time. At this time all are effectively fed a complete diet. Most days they are fed a restricted ration (they would eat more if offered). When weather gets cold, then I put out enough feed so it always present (free-choice access) and most of those days, except immediately following an abrupt weather change, they do consume more. When weather becomes consistently cold and below about 5 F, then I have a way to get them to consume more than they would by simply having free-choice access. What I do is go out near end of day when birds at finished consuming the complete ration as they are effectively full on that, then I toss some shell corn (not cracked or ground) which has large and easily to see morsels that seem particularly easy to consume. Then by weight, they will consume 10 to 25% more food than they would by consuming the complete feed mixture alone.
Based on read of peoples accounts on this site, most people provide free-choice access year round and almost always with a complete feed. For my approach to work with such a strategy, if following the more common feeding regimen, then you need to make certain the feed stuff you provide later is not part of the regular diet and comes in larger morsels.
