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Journal of Animal Production Advances
Egg Quality Deffects: Types, Causes and Occurrence: a
Review
King’ori A. M.
J Anim Prod Adv 2012, 2(8): 350-357
Online version is available on: www.grjournals.com

ISSN: 2251-7677
KING’ORI
Egg Quality Deffects: Types, Causes and
Occurrence: a Review
A Review
King’ori A. M.
Egerton University, Department of Animal Sciences. P.O. Box 536-20115, Egerton, Kenya.
Abstract
Poultry egg quality defects are broadly classified as external or internal. About 10% of the total eggs
produced are downgraded due to external defects while 1% is due to internal defects. External defects include
shell quality, cleanliness, shape, texture and soundness. Egg quality defects lower the grade, consumer appeal,
storage/shelf life, hatchability, increase egg breakage and cost of packaging. Internal quality defects are in the
yolk and albumen. They occur in the form of blood and meat spots, double yolks, mottled and discoloured
yolks, rotten eggs, watery whites, discoloured whites and round worms in eggs. About 5-7% of eggs produced
do not reach the consumer; 2-3% of the damage is due to problems during laying and 3-4% during the process
after laying. No single factor is usually responsible for egg quality deffects. Factors related to egg quality
defects include nutrition, health, flock management, environmental conditions and breeding. It is therefore
important for the egg value chain players to understand the various types of egg defects and their causes. This
will enable them device ways and means to minimize them, hence improve egg quality.
Keywords: Poultry eggs, quality, shell, yolk, albumen.
Corresponding author: Egerton University, Department of Animal Sciences. P.O. Box 536-20115, Egerton, Kenya.
Received on: 25 Jul 2012
Revised on: 06 Aug 2012
Accepted on: 15 Aug 2012
Online Published on: 31 Aug 2012
350 J. Anim. Prod. Adv., 2012, 2(8):350-357

EGG QUALITY DEFFECTS: TYPES, CAUSES AND OCCURRENCE …
Introduction
Egg quality is a general term that relates to
various external and internal standards that are
imposed on the eggs (Koelkebeck, 2003). Some of
these standards are based on subjective measures of
egg quality and some are based on a more
quantitative measure of egg quality. Egg quality has
an influence on egg acceptance or rejection by the
consumer. Egg quality defects are deviations in
external and internal standards of the egg that affect
the quality. Exterior quality includes egg weight,
egg shape, colour, shell thickness, shell weight,
shell density, texture, egg surface area, and
cleanliness (USDA, 2000; Hussain, 2011). The eggs
should be uniform in colour, size and shape. The
shell of each egg should be smooth, clean and free
of cracks. Egg weight, shape and colour are external
characteristics that influence grading, price,
consumer preference and hatchability (King’ori,
2011; 2012). Poor eggshell quality has been of
major economic concern to commercial egg
producers (Washburn, 1982; Roland, 1988).
Information from egg grading facilities indicates
that 10% of eggs are downgraded due to egg shell
quality deffects. Internal quality refers to egg white
(albumen) cleanliness and viscosity, size of the air
cell, yolk shape and yolk strength and involves
functional, aesthetic and microbiological properties
of the egg yolk and albumen. The proportions of
components for fresh egg are 32% yolk, 58%
albumen and 10% shell (Encyclopedia Britannica,
2012). Egg albumen is the clear liquid contained
within an egg. Its primary purpose is to protect the
egg yolk and provide additional nutrition for the
growth of the embryo. It is rich in proteins and
contains almost no fat, unlike the egg yolk, which
has a high fat value. The egg yolk is the yellow
spherical part of an egg that is surrounded by the
albumen. It is the part of the egg which feeds the
developing embryo. The poultry egg is of a high
nutritional value to man that is mainly attributed to
egg albumen and egg yolk which are the edible
components. They supply all essential amino acids
for humans, and provide several vitamins and
minerals, including retinol (vitamin A), riboflavin
(vitamin B 2 ), folic acid (vitamin B9), vitamin B6,
vitamin B12, choline, iron, calcium, phosphorous
351 J. Anim. Prod. Adv., 2012, 2(8):350-357
and potassium. The egg has chemicals and
components (Froning, 1998) that have multiple uses
in biotechnology, chemical, food, pharmaceutical
and art (painting and photography) industries (Egg
Tempera painting, 2011; Germadios et al, 1996;
Messier, 1991).
In the production of poultry eggs, the aim is to
produce eggs with a high hatchability, consumer
preference, and of the best grade that fetch the
highest price (King’ori, 2011, 2012). However,
there are certain defects that affect negatively the
external and internal quality of the egg causing
losses to the producer, retailer and consumer. It is
therefore important to understand the external and
internal egg defects, their causes and economic
importance. Understanding the various egg quality
deffects and their causes will assist in designing and
implementing measures to minimize their
occurrence, hence reducing losses in the egg value
chain. This paper reviews the egg quality defects,
their causes, possible solutions and economic
importance.
Types of Egg Deffects
External defects
Exterior measurements (i.e. measurements
made without breaking or piercing the shell) have
traditionally been done by visual inspection of the
outer surface of an intact egg, to search for cracks,
and by candling. However, a system with a high
precision using a laser scan to detect cracks,
pinholes, and thin regions in the shell has been
developed - U.S. Pat. No. 5,615,777 (Or-Yehuda,
2007). External egg quality deffects include shell
quality, cleanliness, shape, texture and soundness
(Jacqueline et al, 2011).
Shell quality
To the human eye, the shell of the egg appears
to be a homogeneous structure with uniform
composition throughout. When observed under high
magnification, the structure is extraordinarily
complex. It has at least six significantly different
layers beginning with two shell membranes between
the albumen and the interior surface of the shell.
These layers are followed by three regions of
calcified materials, and completed with a thin
organic material on the outer surface called the

KING’ORI
cuticle (Bell, 2007).Within the different layers are
crystalline interfaces, hundreds of hidden fault lines,
and thousands of pores (tiny tunnels which travel
from outer to inner surfaces of the shell). The small
amount of organic matter mostly consists of matrix
proteins (mixture of proteins and polysaccharides
rich in sulphated molecules) and shell pigment. The
matrix proteins are critically important in
determining the egg shell structure and serves as
foundation for the deposition of calcium carbonate
during the mineralization process (Burley et al.,
1989; Lavelin et al., 2000; Gupta, 2008). Without
the matrix proteins, the crystal structure would be
too brittle to keep its form.
The chicken eggshell is 95-97% calcium
carbonate crystals, 0.3% phosphorous and
magnesium and traces of sodium, potassium, zinc,
manganese, iron and copper and organic matter
(Arias et al., 2001; Nys et al., 2004; Hunton, 2005;
Neospark, 2012)). The structure and composition of
the avian eggshell serves to protect the egg against
damage and microbial contamination, prevention of
desiccation, regulation of gas and water exchange
for the growing embryo, and provides calcium for
embryogenesis. The eggshell should be as strong as
possible to maximize the number of eggs reaching
the consumer. No single factor is usually
responsible for egg shell quality. Factors related to
eggshell quality include nutrition (the nutrient
balance and intake levels of the ration), health (the
flock’s general health and previous health history),
flock management and its age, environmental
conditions and breeding (the strain and breed of the
flock) along with other factors (Bell, 2007;
Neospark, 2012). About 5-7% of eggs produced do
not reach the consumer; 2-3% of the damage is due
to problems during laying and 3-4% during the
process after laying.
Types of Shell Deffects
They include shell thickness, gross cracks,
hairline cracks, star cracks, misshapen egg, pimples,
sand paper, pinhole, leatherly and glossy eggs. The
complexity of structure of the shell gives rise to
differences in breakage in eggs. The crack severity,
shape and length are results of variations in the
structure with fractures occurring at the points of
least resistance (Bell, 2007). Shell deffects account
for 0.5-5-6% of total production. Nutrition plays a
key role in maintaining egg quality. The hens
should be offered a balanced ration. Vitamin D,
calcium, phosphorous, manganese, copper and zinc
play a major role in maintaining the integrity and
shell quality. Excess or reduced concentration of
phosphorous, chlorine, or mycotoxin contamination
affects the availability of calcium and vitamin D.
Calcium and phosphorus balance is critical for
proper egg production and eggshell quality. Layer
ration should be formulated with correct amount of
calcium and phosphorus (usually 3.5 - 4.0%
calcium, 0.35-0.40% phosphorus).Numerous factors
affect the functional quality of the egg shell mostly
prior to egg laying. The thickness of the shell is
determined by the amount of time it spends in the
shell gland (uterus) and the rate of calcium
deposition during shell formation. If the egg spends
a short period in the shell gland, the thickness will
be less (Neospark, 2012). Also, the time of the day
when the egg is laid determines the thickness of the
shell. In general, the earlier in the day or light
portion of the photoperiod, the thicker the shell will
be. Intestinal absorption of calcium in the diet is
about 40% when the shell gland is inactive, but
reaches 72% when active. This time closely
coincides with late afternoon or the dark hours for
the layer. Having higher calcium levels in the gut
during this time is important to ensure calcium is
being taken from the diet and not bone.
Shell quality affect consumer appeal,
packaging, egg breakage, storage/shelf life, and
hatchability (Rogue et al., 1994; King’ori, 2011).
An egg shell that is smooth is desirable because
rough shelled eggs break more easily. Large sized
eggs usually break more easily than small ones
because the hen is genetically capable of placing
only a finite amount of calcium in the shell
(Neospark, 2012). Reduction in shell quality lowers
egg shelf life, hatchability and increases breakage.
Shell thickness and porosity regulate the exchange
of carbon dioxide and oxygen between the
developing embryo and the air during incubation
(Rogue, 1994). Shell thickness has significant effect
on moisture loss during storage and incubation
(Bennett, 1992). Thin shelled eggs loose more
moisture than do thick –shelled eggs, causing
352 J. Anim. Prod. Adv., 2012, 2(8):350-357

EGG QUALITY DEFFECTS: TYPES, CAUSES AND OCCURRENCE …
difficulty during hatching (Rogue et al, 1994) and
deterioration on quality for table eggs.
Viral infections (Infectious bronchitis (IB),
Newcastle disease (ND) and Egg drop syndrome
(EDS)) can lead to loss of shell colour, as well as
egg deformities and a reduction in egg numbers
(Thear, 2005). IB virus causes soft/rough shelled
eggs, discolouration and wrinkling of the shell. Egg
drop syndrome (EDS) is a viral infection that results
in a reduced number of eggs, as well as an increased
number of pale-shelled eggs. EDS virus affects only
the shell gland but with ND or IB, every portion of
the reproductive tract can be affected. The
roughness of the egg shell increases with age and
when serious may result in some downgrading.
Molting corrects the problem to a degree, but when
flocks are kept in lay beyond 30–40 weeks, many
eggs become very rough and consumers may find
this displeasing. The hen loses her ability to
mobilize calcium from the bone, and is less able to
produce the needed calcium carbonate. The
absorption and mobilization of calcium decreases to
less than 50% of normal after 40 weeks of age. The
practice of "forced" or "induced" moulting has been
shown to improve shell quality in all ageing flock.
Following the moult, egg specific gravity, shell
weight, shell thickness and percentage shell are
either the same as they were prior to the moult, or
had improved, for all strains. Induced moulting
improves egg shell breaking strength in all strains.
Use of certain chemotherapeutic agents can affect
the intensity of pigmentation. Sulfa drugs affect the
eggshell quality. The presence of the coccidiostat
Nicarbazin in the feed can produce paler shells
(Thear, 2005).
Poor housing, high ambient temperature, rough
handling of the eggs will affect the eggshell quality.
Since large eggs are more prone to cracks, the egg
size must be managed through proper nutritional
and lighting management. Eggs from hens in the
3L: 1D (3 days light: 1 day dark) regimen had a
significantly greater shell breaking strength than
eggs from hens in the 16L: 8D (16 hours light: 8
hours dark) regimen. The hens on the 3L: 1D
regimen have longer dark hours when calcium
absorption is highest (Neospark, 2012). Eggshell
quality is somewhat compromised during summer
months. One of the factors contributing to poorer
eggshell quality in hot weather is inadequate feed
intake. Temporary thinning of the egg shell may
occur during periods of high ambient temperature
(above 25ºC) since feed intake is reduced. The
shells quickly regain normal thickness when
temperatures are reduced and feed intake increases.
During heat stress calcium intake is reduced as a
direct consequence of reduced feed intake and this
stimulate bone resorption resulting in
hyperphosphatemia. This inhibits the formation of
calcium carbonate in the shell gland. Also heat
stress reduces carbonic anhydrase (Zinc dependent
enzyme) activity in the uterus. Under heat stress
more blood is shunted to the peripheral tissues with
concomitant reduction in flow of blood to the
oviduct resulting in poor shell quality. The ability of
layers to convert vitamin D3 to its active form is
reduced during heat stress.
During exposure to warm environmental
temperature, the hen reacts by increasing its rate of
breathing (panting) in order to cool itself. This
causes the lowering of carbon dioxide in the blood
and produces a condition termed "respiratory
alkalosis". The pH of the blood becomes alkaline
and the availability of calcium for the eggshell is
reduced. This disturbance in acid-base balance
causes an increase in soft-shelled eggs during
summer. Respiratory alkalosis also causes increased
carbonate loss through the kidney resulting in
competition between kidney and uterus for
carbonate ion, consequently resulting in poor
eggshell thickness.
The shell is formed by the activity of cells
lining the oviduct and uterus. Under stress the
secretions of these cells become acidic and the cells
can be damaged or destroyed. In extreme cases,
stress induced effects can result in eggshells that
have excess deposits of calcium - a sort of powdery
"bloom" on the surface and result in misshapen
eggs. The presence of parasitic red mites that
emerge at night to feed on the perching hens can
have a debilitating effect on the birds, leading to
anaemia, poor shell thickness and loss of egg
colour. The presence of parasitic worms can also
debilitate the hens to the extent that their nutritional
intake is affected that leads to the production of
eggs with deffects. A sudden disturbance to the
normal routine may result in a hen retaining the egg
353 J. Anim. Prod. Adv., 2012, 2(8):350-357

KING’ORI
within the shell gland area of the oviduct for a
longer than normal period. During this time a very
thin layer of extra calcium is deposited on the egg,
producing a greyish, bleached outlook (Thear,
2005). Release of stress-related hormones will
result in the production of pale brown-shelled eggs
(Hughes et al., 1984). Relocation, such as
movement from one type of housing to a completely
new housing environment, stresses the hens and can
produce severe visual defects of the egg. It is known
to increase the incidence of calcium coated and
checked (misshapen) eggs.
Internal defects
These include defects on the yolk and albumen.
Assessment of Interior egg quality involves
breaking the egg to inspect its contents. Two
interior measurements in common use are the
measurement of yolk color using the Roche Yolk
Color Fan, and the measurement of Haugh units
which also characterize the freshness of an egg
(USDA, 2000; Or-Yehuda, 2007). The Roche Yolk
Color Fan has 15 sample colors, ranging from 1 (the
lightest) to 15 (the darkest), which are visually
matched to the color of the yolk. Internal egg
deffects occur in the form of blood and meat spots,
double yolks, mottled and discoloured yolks, rotten
eggs, watery whites, discoloured whites and round
worms in eggs (Optimum egg quality, 2010).
Occurrence of blood and meat spots is revealed by
candling. Candling reveals most of the spots, but
brown eggshell hampers selection in brown chicken
lines. Estimated frequency of blood and meat spots
in brown layers is about 18% whereas it is 0.5% in
white egg layers (Honkatukia et al., 2011). Several
factors are known to increase the incidence of meat
and blood spots: genetic background, low level of
vitamin A and/or D, stress or infections. Internal
egg quality involves functional, aesthetic and
microbiological properties of the egg yolk and
albumen. Meat and blood spots in addition to being
an aesthetic and ethical problem, they may increase
the risk of infections such as salmonella (Smith et
al., 2008) and reduce hatchability of eggs
(Bermudez et al., 1993). Blood spots are droplets of
blood found usually on the surface of the yolk
(Shirley, 1965). Meat spots appear as red, brown or
white spots in the albumen. They are either pieces
of tissue from reproductive organs or blood spots
that have changed colour due to dilution. They
emerge during the ovulation process in the ovary or
later in the oviduct. Blood on the yolk originates
from bleeding of the small vessels in the ovary or in
the oviduct (Shirley, 1965). Meat spots in the
albumen can be formed from a bit of reproductive
tissue while the egg is passing through the oviduct.
As an egg ages, the yolk takes up water from the
albumen, which in turn dilutes blood spots and
makes them look like meat spots. In general the
frequency of blood and meat spots is less than 1%
in all eggs laid in commercial lines (Smith et al.,
2008). The incidence of spots seems to increase
when the hen ages (Bustanyet al., 1987). Increased
frequency also appears at the start of laying.
Different factors, including nutritional,
environmental and heredity, trigger the incidence of
spots. Probably the most important nutritional factor
is a lack of vitamins A and D (Sauter et al., 1975;
Bermudez et al., 1993; Sutcliffe et al., 1998). When
the supply of vitamin A is sufficient, the chicken
has a low probability of having blood spots (Becker
et al., 1973). Environmental factors, like sudden
loud noises, temperature changes and infections,
induce an increase in the incidence of spots
(Campo, et al., 1998; Deaton, et al., 1986).
Double Yolk eggs appear when ovulation
occurs too rapidly, or when one yolk somehow gets
stuck before shelling and is joined by the next yolk
(2011 PoultryHelp.com). Double yolk eggs may be
laid by a pullet whose productive cycle is not yet
well synchronized. They're occasionally laid by a
heavy-breed hen, often as an inherited trait. They
are usually bigger than the ordinary (normal) egg.
No-yolk eggs (yolkless eggs) are called "dwarf",
"wind" eggs. Such an egg is most often a pullet's
first egg, produced before her laying mechanism is
fully developed and is usually smaller than the
ordinary egg. In a mature hen, a “wind” egg is
unlikely, but can occur if a bit of reproductive tissue
breaks away, stimulating the egg producing glands
to treat it like a yolk and wrap it in albumen,
membranes and a shell as it travels through the
oviduct (2011 PoultryHelp.com). A double shelled
egg or an egg within an egg appears when an egg
that is nearly ready to be laid reverses direction and
gets a new layer of albumen covered by a second
354 J. Anim. Prod. Adv., 2012, 2(8):350-357

EGG QUALITY DEFFECTS: TYPES, CAUSES AND OCCURRENCE …
shell. Sometimes the reversed egg joins up with the
next egg and the two are encased together within a
new shell. Double shelled eggs are so rare that it is
unknown exactly why they happen.
Some eggs may have an unusual or
unacceptable odour or taste, although their
appearance is normal (Optimum egg quality, 2010).
They differ from rotten eggs, which are obviously
defective and smell putrid. Off odours and flavours
are rare in fresh eggs stored correctly. They will
occur due to poor storage conditions (long storage
period, high temperature, and presence of strongly
scented materials in egg store) and use of strongly
flavoured ingredients in the feed. Hens that eat
onions, garlic, fruit peelings, fish meal, and fish oil
will lay eggs with an undesirable flavor. Eggs can
also absorb odors that translate into unpleasant
flavors if they're stored near kerosene, carbolic acid,
mold, must, fruits and vegetables (2011
PoultryHelp.com). Certain bacteria and fungi
growing either on the outside or the inside of the
egg may give an undesirable odour or flavour to the
egg contents without causing noticeable spoilage.
Bacterial or fungal contamination of the egg can
produce rots (black, red, green). The egg looks and
smells putrid when broken out. Under conditions of
good management, the incidence of rotten eggs is
very low; such eggs must be eliminated during
grading, as they have such a detrimental effect on
product image (Optimum egg quality, 2010).
Bacterial and fungal contamination will occur due
to faecal contamination, improper washing
procedures, high storage temperature and humidity,
long storage period and infection of the hen’s
oviduct. The development of watery whites is
chiefly due to the increasing age of the egg. When
an egg broken onto a flat surface has a watery,
spread-out white, this usually indicates that the egg
is stale. The yolk index and haugh unit are the best
indicators of internal egg quality (Isikwenu et al.,
1999). Yolk index is determined as a ratio of the
yolk height to the yolk width. The height of the
white and the weight of the egg are used to calculate
a value in Haugh units on a scale of 0-110; the
lower the value, the more stale the egg. The higher
the yolk index (Ayorinde, 1987) and haugh unit the
more desirable the egg quality. A minimum Haugh
unit measurement of 60 is desirable for whole egg
sold for the domestic consumer (Optimum egg
quality, 2010). Oiling of eggs within 24 hours of lay
is very effective in slowing down reduction in
albumen quality, but does not replace the need for
cool storage (Jacqueline et al, 2011).
The normal colour of egg white is slightly
yellow-green but may be discoloured to yellow,
green or pink which is objectionable (Optimum egg
quality, 2010). However, this problem is rare.
Excess riboflavin in the diet causes egg white to
turn green while cyclopropene fatty acids in
cottonseed cause the white to turn pink after
storage. Omission of xanthophylls in the diet will
lead to pale yolks (Esonu, 2006). Pale yolks can
result from any factor which alters or prevents the
absorption of pigments from the diet or the
deposition of these pigments in the yolk. The
inclusion of more than 5% cottonseed meal in a
layer diet will result in olive or salmon coloured
yolks (Esonu, 2006). Mottled yolks (with many pale
spots and blotches which vary in colour, size and
shape), occur when the contents of the albumen and
yolk mix as a result of degeneration and increase
permeability of the vitelline membrane (Amiri Andi
et al., 2006). The anticcocidial drug, Nicarbazin, has
been shown to cause yolk mottling when fed at a
concentration of 0.005% or greater in the diet. The
degree of mottling is not the same in all eggs, and
not all hens respond the same way to Nicarbazin.
However, a direct relationship exists, however,
between the duration of feeding Nicarbazin, the
level of Nicarbazin in the diet, and the incidence of
mottled eggs. Deworming drugs, such as Piperazine
and dibutyltin dialaurate, have also been reported to
cause yolk mottling (Jacqueline et al., 2011).Some
eggs may contain one or more roundworms, though
the incidence is quite rare. Roundworms are internal
parasites and migrate from the cloaca to the oviduct,
where they may be enclosed in the egg (Optimum
egg quality, 2010). This egg defect can be prevented
by regular deworming and good hygiene.
Conclusions
Egg quality is influenced by nutrition, breed,
climatic factors, flock management (age, housing,
disease control), and post-lay handling of eggs. Egg
quality is determined by the external (shell) and
355 J. Anim. Prod. Adv., 2012, 2(8):350-357

internal (albumen and yolk) quality. The same
parameters are part of the grading criteria.
Therefore, they influence the price of an egg. The
players in the egg value chain must each play their
role in the most efficient way to maximize returns.
For the egg producer, the aim is to produce the
highest number of eggs of the best grade. This will
be achieved by keeping the right breed, offering the
right nutrition and practicing the right flock
management. For the supply chain, they must
supply right inputs demanded by the egg producer
and marketer. The consumer demands are variable
depending on their uses for eggs-table,
confectionery, hatching, laboratory etc. Consumer
concerns are conformity to the set quality standards
(freshness, colour: shell, albumen and yolk), shell
shape and strength and nutritive value). Therefore,
there has to be an efficient flow of feedback
information through the value chain to ensure
production, marketing and consumption of eggs of
the set quality standards. Affordable and accurate
equipments for assessment of egg quality should be
designed, customized and produced for use by the
different players in the egg value chain.
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