Another fallacy: scratch does NOT keep the birds warm in winter! It's a treat, low protein, meant to be fed in small quantities occasionally. Helps to train them to come when called, that's it. Adding it to layer feed is not helpful!
An all flock feed, like Purina's 20% protein Flock Raiser, for example, meets everyone's needs with the oyster shell on the side. Birds not in lay shouldn't eat layer feed, and again, adding scratch decreases their protein and other nutrient levels much lower.
'Zillions' have been spent learning the nutritional needs of chickens, and trying to 'improve' their diets by mixing whatever other ingredients, not an improvement. Listen to Stormcrow!
Mary