One chicken seems to have less feathers on her neck and so she looks a bit sick. Also the tips of the feathers on her head are turning grey or white. Any thoughts on what is happening? It is an Americauna and about 1.5 years old hen. It is about 10 Celcius 50F here at night and probably 15 C 60F in daytime and raining lots. I recently treated her with Dusting Powder 5% Carburyl. I held her by the legs and shook it all over. Pretty hard to miss the head.