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It could just be what you said dry skin or it could be favus(a type of fungus-a pic might help) but that isn't likely because it needs warm spring summer type conditions to be able to grow (moist and warm), depending upon the age their first year most will lay through the winter but every year after they will slow down considerably and some may stop altogether, it is like a dog they will shed their winter coat so they aren't getting took hot come this summer.
Temperature doesn't have as much to do with egg laying as does the length of daylight hours. Days get shorter, birds stop laying. They will also stop laying when they molt. During this time it is normal for the comb to paler and smaller. Are you sure about their age? Most hens will lay through their first winter and don't have a real molt until their second year.
Edited by Davidson5 - 2/23/16 at 5:34pm