I read corn before bed time keep chickens warm as it process during the night. It heat up their body temperature.
I give my chickens corn before bed time every day in winter. A few times a week individually feed them cut out small pieces of ginger or turmeric. They do not eat those themselves that is why I have to feed them individually. They only eat the leaf of those plants growing near the fence. Turmeric and ginger warm up the system.
Sardine in water is the extra protein I got from Aldi, over here it is A$0.90 per can. My chickens love it.
I also rubbed on each of them on the combs, under their wings, and beaks a bit of VetRX. Everything inside the coop smell really cosy.
The vitamins drink, the sardine, the ginger/turmeric, the corn, and the VetRX. It is a lot of work, but it better than treating an illness.