Out of 17 hens, 2 have substantial bare patches on their backs. Yes, I'm slow thinking of this, but the night lows are in the upper twenties, and they free range during the days. Chicken house has a heat lamp over the roost, but should I coat their backs with something? I was thinking of pine tar. "Pecks No More" doesn't last and hour before it is gone, in my experience. Thanks for your advice.