*** I am not a vet, so please seek further advice after reading this article. ***
The comb is the chicken's primary way of indicating the health of their circulatory system which can be affected by a number of things. The most common being due to parasite infestation. Blood sucking mites can cause anemia in chickens which is evident in the comb colouring. Always investigate parasite causes first.
But there are more reasons beyond parasites that can cause a purple or blue comb.
Circulatory or Respiratory issue: The blueness is due to blood either not having enough oxygen or because the blood isn't being circulated properly.
Respiratory Disease or Cardiac Problems: This will require further veterinary investigation to confirm this diagnosis. Age, genetics, health history and cleanliness of their environment will be factors.
Chilling (Cold Weather) is one way to cut circulation to the comb.
Unclean Shed: The build of ammonia in the chicken shed from droppings can interfere with their breathing often causing a really dark comb. Giving the shed a daily light clean and making sure there is good ventilation should help prevent this.
Blue Comb Disease: Avian Monocytosis
- Loss of appetite.
- Crop distension.
- Dark comb and wattles.
- Watery diarrhoea
- Drop in egg production
Keep your chickens really well hydrated, with CLEAN water and may even some electrolytes in the water.
Please seek advice from your vet for a clear diagnosis.