Chickens in the Cold

I've been raising chickens in the harsh climate of Northwestern Wisconsin long enough that I've learned a few things about keeping them through our cold winters. While many would think the cold would be the biggest problem in my unheated coop, aside from a few frozen combs (which don't seem to have any permanent detrimental effect on the birds) and perhaps, in really extreme weather, frozen feet (which I've encountered once, when it was -40F for more than a few days), I've found that it's really the thaw after the freeze that causes the most harm. It's usually in the spring, or in an early thaw (like today), that I see problems.
While the bedding is frozen, biological action pretty much stops, but once it thaws, parasites and pathogenic bacteria quickly start becoming a problem. I've dabbled in the deep bedding method, with disastrous results (I lost an entire flock of 40 one-year-old hens one spring). Since then, I've either added bedding weekly (a contractor-sized bag of leaves for my 10x12 coop) or, if there's a thaw in the forecast, shoveled out the barn entirely (and of course spread it right on the snow-covered garden as a sheet mulch). I've started going by the adage, "If you can smell ammonia, it's time to clean it out." This seems to keep my flock much healthier.
Plus of course, it's good exercise!