Ditto Dat!
When it's near zero for extended periods, I give a weekly dose of Electrolytes/Vitamins.
It definitely perks up their consumption of water and feed.
https://www.backyardchickens.com/articles/aarts-extreme-weather-spiel.75893/
Mine get the same feed all year around.
Corn will not help keep them warmer, most feed is mostly corn anyway.
They need to go to roost with a full crop of quality feed, which they will do all by themselves. Digestion of that will 'create heat'.
The only thing different I feed is during long...