The following article goes in depth trough the main problems that may affect the eggshell formation process, and we mention their main causes.

Cracked or perforated eggshell

Weakened eggshell strength is due to excessive heat, salty drinking water, calcium or vitamin D deficiencies and fungal infections. The incidence increases as long as hens get older.

Shell-less eggs

The egg content is only protected by the outer membrane. The lack of eggshell may be caused by:��

• Immature eggshell gland in young laying hens
• Deficiencies in calcium and vitamins E, B12 and D, and phosphorus and selenium
• Diseases such as Newcastle disease (NDV), Avian Infectious Bronchitis, Avian Influenza, Egg drop syndrome
• Parasites or mycotoxins
• Stress causing premature laying

Deformed or irregular eggshell

This refers to eggs that differ from their normal shape and/or size. It can be the result of an immature eggshell gland, diseases – Avian Infectious Bronchitis, NDV and Avian Infectious Laryngotracheitis – or stress induced by coop overpopulation.

Asymmetric or body-checked eggs

These eggshells crack during the calcification process, which are consequently repaired by the deposition of a calcium layer above the crack right before the laying. This event tend to occur when the lighting program is incorrect -more than 15 hour light exposure- and also due to stress by coop overcrowding. Its incidence may increase in senior specimens.

Corrugated eggs

Wrinkled eggs appear when the egg membrane is thinner than normal��due to a double/multiple ovulation. By having two yolks the membrane has to stretch to make space for the extra yolk. In these cases calcium will be deposited and will develop in a corrugated eggshell. Possible causes are:

• Extra-large eggs, usually two yolk eggs or multiple yolk eggs
• Diseases such as NDV and Infectious Bronchitis
• Excessive use of antibiotics
• Copper deficiency or excess of calcium
• Defective eggshell gland or hereditary factors

Shell total or partial depigmentation��

Shell pigments have been described as porphyrins or ooporphyrins. These are cyclic compounds consisting of four pyrrole rings and they come from the degradation of haemoglobin when red cells are destructed in the liver. Most brown eggs contain these porphyrins or, concretely, protoporphyrins. Basically, porphyrin or protoporphyrin IX is deposited on the white eggshell while on its formation.

It is also believed that these pigments could come from or be synthesized “de novo” in the uterine gland, but it has not yet been proved. A fact that it has already been demonstrated is the cyclic accumulation and release of the pigment from the epithelial cells of the uterine gland.

Because of the origin of porphyrins, it stands to reason that causes that can damage the liver or alter the hepatic metabolism may also have an effect on egg pigmentation. Processes causing anaemia and, therefore, reducing erythrocyte or haemoglobin levels may also produce paler shells.

Main causes are usually related to poor nutrition, parasites or the use of drugs that affect the liver.

• Poor nutrition: deficiency in nutrients such as protein or certain minerals can affect pigmentation or formation of the eggshell
• Parasites: roundworm, capillarias and red mites infestations can affect the liver and cause paler eggshells
• Drugs such as Nicarbazin or other antiparasitics. If nicarbazin is administered at a dose of 5 mg per day, approximately, it can damage the liver and affect the normal production of porphyrins. Consequently, eggshells appear show different colour intensities and uneven-pigmented spots within the next 24 hours after drug administration. The pallor of the shell can also occur after prolonged treatments at high doses, such as 600 to 800 ppm of tetracycline.

Other possible causes for eggshell depigmentation may be:

• Oviduct damaging diseases that indirectly affect egg production. Total production declines and shells becomes thinner, irregular and abnormally pale – Infectious Bronchitis, Newcastle disease, egg drop syndrome and Avian Influenza.
• Older hens tend decrease in their laying intensity and deliver paler eggs more often. It may be caused because the same amount of pigment is deposited on a wider surface, as eggs become larger with age and less pigment is synthesized.
• Retention in eggshell gland is related to stress and the subsequent abnormal deposition of calcium carbonate is a major cause of pale eggs in older hens.��Main factors that may cause stress in the henhouse are high specimen density, handling and loud noises. These can lead to adrenaline release, which is responsible for causing a delay in��oviposition or disrupting the formation of the cuticle.
• Excessive exposure to sunlight and high temperatures: eggshell alterations may occur more frequently in warmer seasons.