In the previous article we talked about the process of formation of the eggshell, but in this chapter we will focus on classify some of the different eggshell defects and we will mention their causes.
- Cracked or perforated eggs: The reduction of the eggshell strength is due to: excessive heat, brackish water, calcium or vitamin D deficiencies and fungal infections. The incidence increases while hens are getting older.
- Shell-less eggs: The egg content is only protected by the outer membrane. These shell-less eggs are produced because of:
- Immature eggshell gland in young laying hens
- Deficiencies: calcium, vitamins E, B12 and D, and phosphorus and selenium.
- Certain diseases such as: Newcastle disease, Avian Infectious Bronchitis, Avian Influenza, Egg drop syndrome.
- Parasites or mycotoxins
- Stress that causes premature laying
- Deformed or irregular eggs: This refers to eggs that differ from the normal or their size is too large or small. These eggs can result from: Immature eggshell gland, diseases (Avian infectious bronchitis, Newcastle disease and Avian Infectious Laryngotracheitis) or it also can be caused by stress or crop overpopulation.
- Asymmetric or body checked eggs: These eggshells crack during the calcification and this crack is repaired by the deposition of a calcium layer above the crack, this will occur before the egg laying. This event, usually occurs when the lighting program is incorrect (more than 15 hours of light), when there is overcrowding or stress and its incidence increases with age.
- Corrugated eggs: These eggs are completely wrinkled, this happens when the egg membrane is thinner than normal, due to a double ovulation. Having two yolks, the membrane has to stretch more to cover the extra content of the egg, thus the egg won’t be round enough and the membrane will be corrugated. Here the 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: Newcastle disease and Infectious Bronchitis
- Excessive use of antibiotics
- Copper deficiency or excess of calcium
- Defective eggshell gland or hereditary factors
In the previous article, we talked about some of the major defects which could appear in the eggshell, such as cracks or holes, deformations and irregularities, corrugations or dents and the absence of shell “per se”.
In this article, we will focus on describing the total or partial depigmentation of the shell and determine its causes.
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 it is on formation period.
It is also believed that these pigments could come or synthesized "de novo" in the uterine gland but it has not been already shown. The fact that it has 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 hepatic metabolism may affect pigmentation of the egg. Processes causing anaemia and therefore reduce erythrocyte or haemoglobin levels may also produce paler shells.
Among these causes are: poor nutrition, parasites or some 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: A large roundworm infestation or capillarias and red mites, can affect the liver and cause paler eggshells.
- Drugs such as nicarbazin or other antiparasitic. 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, egg shells appear with different intensities of colour and uneven pigmentation spots and this may happen in the next 24 hours. 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 of depigmentation of the eggshell are:
- Different diseases that cause damage to the oviduct, and indirectly affecting egg production. The total number of egg production declines and shell becomes thinner, irregular and abnormally pale: infectious bronchitis, Newcastle disease, egg drop syndrome and Avian Influenza.
- Old hens: as the hen ages, there is a decrease in the intensity of the pigment of the shell and therefore paler eggs are produced. It may be because the same amount of pigment is deposited on a wider surface, as eggs become larger with age or it just that less pigment is synthesized.
- Stress: retention in eggshell gland is related to stress, and therefore the subsequent abnormal deposition of calcium carbonate is a major cause of pale eggs in older hens.
The factors that cause stress in the henhouse are: high density, handling and / or the loud noises.
These factors can lead to the release of adrenaline. Adrenaline is responsible for causing a delay in
oviposition or disrupting the formation of the cuticle.
- Exposure to sunlight and high temperatures: the alterations of the eggshell may occur more frequently or suddenly in warmer seasons.