A chicken should have a nice, red comb and when it starts to look more like a pale pink, something is stressing the bird and it's time to take care of it. Here are some possibilities with some questions to help you narrow it down:
- Mites - Did you check their vent and notice any moving black bugs?
- Worms - Have you noticed any worms in their stools and do they have a lot of access to earthworms?
- Marek's Disease - Are they having any trouble walking?
- Coccidiosis - Have you noticed any blood in their stools?