For the main diet, I would rely on a complete poultry ration that is formulated for the birds’ age and stage of production rather than trying to mix everything myself.
Chickens should receive a balanced prepared feed containing the necessary vitamins, minerals, and protein, with laying hens also needing adequate calcium and grit.
A helpful American overview on how to feed chicken also notes that fruits, vegetables, grains, and insects can be part of what chickens eat.
I would treat kitchen scraps and scratch grains as extras instead of letting them replace the nutritionally balanced feed.
