The color of the eggshell depends on several pigments, and especially on ovoporphyrins (avian protoporphyrins).

Protoporphyrins are waste products obtained from the recycling of haemoglobin and its deposit on its eggshell increases for the following reasons:

1. Lack of calcium in alimentation. Birds need to harden its eggshell by depositing ovoporphyrins. In this case, it must be accompanied to other symptoms such as existence of eggs in Farfan, alterations in the keel, bone density loss of femur and also can be confirmed by the weight loss of the eggshell (less than 5.5gr).

2. Viral infections which affect the oviduct such as infectious bronchitis. In this case must be accompanied by increased size and liquid content of atrophied left oviduct in hens as well as the presence of eggshells with longitudinal wrinkles. Maybe birds are vaccinated so we can talk about subclinical infection.

3. Viral infections which increase the destruction of red corpuscles such as avian infectious anemia.  In this case must be accompanied by retardation in growth and paleness. Maybe birds are vaccinated so we can talk about subclinical infection.

4. Hepatic intoxications by antiprotozoal and antioxidants which produce the overproduction of porphyrins. They must be accompanied by other symptoms such as hepatomegaly and discoloration of the liver, renal alterations and ascites. It can be an over dosage or accumulation (antioxidants in fat) or the presence of antiprotozoal which have introduced improperly in the chain of food production.