Do chickens get cold?
This question sparks a lot of debate. Here's our take:
Chickens are not like house pets - they don't have the same requirements for heat. They are also covered in thick layers of downy feathers that are designed to keep them comfortable in the elements that Mother Nature throws at us. Chickens, do not require heaters in the winter in their coop.
That being said - you will want to pay good attention to your breed of chicken, quantity of chickens, egg production, and coop structure before you decide to keep the lights out.
We have a flock of 30 chickens these days... (that escalated quickly). In the winter time, they don't like to leave the coop often when it snows. When they cuddle in the coop together, it actually gets pretty toasty from all the body heat they each put off. We personally have enough chickens that the variety in breeds in the flock doesn't really make a difference. I say that because we have a mix of hardy, all weather breeds, as well as some more fragile ones like the silkie chickens. The silkies usually do better in warmer climates, but the flock variety seems to help them thrive and keep warm, allowing us to keep them. On their own, it might not be the case. When selecting chicken breeds, it is always good to take these factors into consideration.
If you do opt to turn out the heat lamps and let the chickens do their thing, then you may notice that your egg production will slow wayyy down. Your dozen a week might get measly. The reason being is that chickens, are in tune with nature. Their cycle relies on daylight and warmth so the less of that there is, the less they will be willing to produce. Don't hold it against them - they can't help it. To get your egg fill it might be a good idea to pickle some or freeze some egg based dishes in the fall if your chickens do slow down. Alternatively, you can run a heat lamp for a while each day to give the hens a hand. We do this, and it does keep our production up. We are still averaging about 6 dozen eggs a week. I would highly recommend only using a red heat lamp, as opposed to the white light, as red light is more calming and won't confuse your rooster about the time of day if you have one.
You can also encourage your chickens to free range on warmer winter days, and throw some cracked corn around the yard for them to peck at. Like us, a healthy amount of excersize is good for them and their egg production. The cracked corn is also good for them in the winter as it contains a higher calorie count, needed to help them keep their body temps up. Adding some oyster shell (you can buy it by the bagfull at your local Tractor Supply) in their feed is also great for egg production as they will need higher levels of calcium in the winter to keep producing.
Last but not least is of course the structure itself - if it is breezy inside, consider throwing a tarp over it for the winter, or placing a topper on it (out of wood or metal or plastic) to keep any snow melt out. Just make sure they always have access to fresh air, water, and ample food.
Do make sure that your heat lamp is safely set and be weary of the dangers of coop fires if left unattended or somewhere where it could be knocked down.
Replace the bedding in the coop frequently, to keep things as clean as possible. All that time spent in-doors and with cold, wet, snowy feet can lead to sickness for your flock if they are not well kept.
To foster another heat sorce, consider the deep bedding method for your bedding shavings!
A tablespoon of apple cider vinegar in their drinking water once a week will also encourage healthy chickens.
Again, this is just what we do and we have found it works for our flock. Let us know if you have any other tips you'd recommend to keep chickens from being chilly!