How much land do you have? Rotational forage where you let them into an area for a while combined with planting specific forage blends could cut back on the amount of feed they will require. My summer feed bill is a half to a third of the winter bill.
Need to figure out how to harvest and store stuff for the winter.
Seasonal differences in feed bill I see are due to two factors. First is as you assume where birds get more nutrition from forage. Second is birds require more to stay warm. My birds can roughly double feed intake when it gets cold although that additional intake need not come from additional complete ration.