I think feed has alot to do with egg production, growth of chickens etc. I think as long as you give them a well balanced healthy diet, your egg production and quality will greatly improve. My chickens are free range (2 1/2 acre yard) during the day, they have organic feed available to them 24/7. But my girls and my rooster like treats in late afternoons. I generally give them fresh spinach or kale and my girls always produced eggs with hard shells.. But now that it's winter, nights getting below freezing, I need to add some fat to their diet. Problem is, they don't like anything I've tried so far (pumpkin, freeze dried bugs etc.) So at this point I'm stuck on how to add some fat to their diet, and while they have a coop to sleep in at night, with lots of bedding, I still worry that they still get to cold in early mornings, windy days. So if anyone has any ideas on what else I can try to add fat, I'd appreciate it.