Diagnosis: The comb, and also sometimes wattles will turn black, starting at the tips / ends and moving inwards. These black bits will then shrivel up and drop off. Birds (male and female) with big combs and wattles are the most susceptible. A Rooster With Frostbite to the Comb and Wattles
Cause: Cold temperatures - way below freezing.
Mortality: None. Animals affected can still be used for breeding and live a perfectly normal life, but cannot be shown.
Treatment: To prevent frostbite, you can rub vaseline over the combs and wattles of birds affected. This will also work in birds in the early stages of frostbite, although to a limited extent. Prevention is better than cure!
Picture courtesy of www.thecozynest.com