This rooster has lost the tips of his comb to frostbite. The Barred Plymouth Rock is very hardy and has enjoyed popularity as a backyard heritage breed for many generations due to it’s toughness and productivity. Still, the combs are the weak spot. Wattles are close enough to the body to stay warm and feet get tucked into feathery bodies when they roost at night. You can try applying Vaseline but I haven’t found that to be something many roosters will cooperate with.
Although I had them in an unheated coop (which is fine if it’s not drafty) he did roam outside and visit the barn to eat grain spilled by the goats. Frostbitten combs are unsightly but they aren’t a major cause of concern and heal easilly without intervention. The blackened skin will fall away without blood or infection, winter being an easy time on wounds due to the lack of flies. The numbing effects of cold and tissue death seem to make this relatively painless. Chickens will complain loudly when something is wrong (a couple of mine complain loudly every time they lay an egg) but I haven’t observed any behavior from a rooster that would indicate distress over a frostbitten comb. Comb pecking during fly season is another story.
To prevent frostbite, use of a heat lamp in the coop helps, although I’ve had chickens that simply don’t both to go under it or wander outside all winter. Ultimately the best bet is to find a breed with small combed roosters, Buckeyes being my hands-down favourite. Hens of any breed are small enough not to have comb issues but they are even tinier on Buckeye hens, which I’ve found means less heat loss and more conservative winter diets.