It's a great question and one that seems to spark a lot of debate. It's good to be concerned. There isn't a ton of research on how cold affects chickens, but I think it's important to review. What we do have suggests that chickens ARE very susceptible to cold stress, despite conventional beliefs.
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That depends on which sources you read. Others describe healthier chickens in unheated housing.
No research here. It looks like the grad student (second author was a grad student, perhaps when it was written) wrote it and the extension educator (first author was that) signed off on it. I've been a grad student... most of their papers (outside of theses) are what the internet says.
"...In essence, low temperature in laying hens altered antioxidant systems and lipid metabolism without inducing stress responses...."
Altered systems and metabolism doesn't necessarily mean harm. People alter their metabolism when they exercise.
Yes, fewer eggs. 6.3 per pullet per week instead of 6.5 over this four weeks. It might be the different temperature. It might be that both groups were acclimated then one had the temperature drop and the other had no change of temperature.
Other studies have shown hens in unheated housing laid more eggs than hens in heated housing under the same management otherwise.
Behind a paywall.
No research. They say they assume chickens are tropical because of red jungle fowl origins. Although they do note the millenniums in cold climates allow for adaptation. I don't think they mentioned a generation is only a year to a few years or anything about how many chickens per year from which selection was made.
They say, "...Once temperatures fall below 20℉ (-7°C), frostbite and hypothermia begin to set in..." Except they don't even at prolonged subzeroF temps in many cases. How much else is not true as much as they say it is? Comfort, ever, at those temperatures might be arguable but frostbite is visible and not subjective.
"For those who closely monitor and provide compassionate care to their bird companions, discomfort in birds is visibly noticeable once temperatures hit around 32℉ (0°C). At this point, birds begin to lose their ability to regulate their body temperature... Signs of hypothermia in birds include shriveled and pale faces, combs and wattles. Birds may tuck their heads into their shoulders and under their wings, and fluff their feathers. They may shiver, huddle together, and become inactive..."
Shriveled and pale faces, combs, and wattles are also signs of not laying due to dark days of winter. Tucking heads into shoulders and fluffing feathers is part of chickens regulating their temperature.
Chickens
can get hypothermia and frostbite, even at relatively moderate temperatures like near 32F. It is a possibility, not the given they portray.
They did get a LOT of things right, though. The importance of ventilation, not using vaseline, adequate water and feed, monitor the chickens,... other things.
Recommending running dehumidifiers so you can leave windows cracked open as you run heaters as soon as the temperature reaches 32F..is just..... Well, I suppose it might help lower humidity. I don't think it would help ammonia levels.
Going down to 19, maybe 17, tonight. Wind gusts 45mph+
