Egg shell quality and egg internal quality are of major importance to egg industry worldwide
Egg quality is a general term which refers to both internal and external quality
External quality is focused on shell cleanliness, texture and shape, whereas internal quality refers to egg white (albumen) cleanliness and viscosity, size of the air cell, yolk shape and yolk strength

internal egg quality

Internal egg quality 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

The egg white is formed by four structures. Firstly, the chalazae, immediately surrounding the yolk, accounting for 3% of the white
Next is the inner thin layer, which surrounds the chalazae and accounts for 17% of the white
Third is the firm or thick layer, which provides an envelope or jacket that holds the inner thin white and the yolk. It adheres to the shell membrane at each end of the egg and accounts for 57% of the albumen
Finally, the outer thin layer lies just inside the shell membranes, except where the thick white is attached to the shell, and accounts for 23% of the egg white

External egg quality

Poor eggshell quality has been of major economic concern to commercial egg producers, Information obtained from egg grading facilities indicates that 10% of eggs are downgraded due to egg shell quality problems. Based on values for the UK, Germany and the USA, it has been estimated that the incidence of broken eggs ranges between 6 and 8%

To maintain consistently good shell quality throughout the life of the hen, it is necessary to implement a total quality management programme throughout the egg production cycle

Exterior egg quality is judged on the basis of texture, colour, shape, soundness and cleanliness according to USDA (2000) standards. The shell of each egg should be smooth, clean and free of cracks. The eggs should be uniform in colour, size and shape

External quality (egg shell quality)

Factor affecting egg shell quality

• Age and bird strain 

As a result of genetic selection , different strains of laying hen vary significantly in egg shell quality and there are clear difference between modern commercial birds and traditional breed of laying fowl
older bird tend to lay bigger eggs and have higher egg output which impact on shell strength 
very young bird have immature shell glands may produce shell-less egg or egg with thin shells
some studies have shown that egg shell quality decrease as bird grow older , egg size increases with increasing hen age at the same time shell weight increase or stay same
the increase in egg weight is not accompanied with increase in shell weight

• Egg shell integrity 

Defects considered under this category include : gross cracks , hairline cracks , star cracks , thin shell , shell-less egg
cracked egg cant be available for retail sale , one of the most abovious reasons for egg shell cracks is mechanical damage egg shell length ultimately affect soundness of shell , with weaker shelled egg more prone to crack and breakage and subsequently microbial contamination 

• Nutrition and water quality 

Each egg shell contain up to 3 gm of calcium .therefore the diet of hen must contain adequate calcium in a form that can be utilized efficiently. (50-70% should be in coarse form and the remainder part in powder form)

The provision of adequate dietary minreral and vitamins  is essential for good shell quality  similarity as water quality vary from country to country . the role of drinking water in mineral and trace element supply shouldn’t be overlocked

Calcium and phosphorus are essential macro mineral 

Minerals with calcium forming significant  component of shell and phosphorus play important role in skeletal calcium deposition and availability of calcium for egg shell formation

Vitamins such as vitamin D are necessary for calcium metabolism and must included in diet , adequate level of vitamin c are essential for normal good health and may help in alleviate the effect of stress , there is also evidence that supplemental vitamin E assist under conditions of heat stress , low level of vitamin A  may increase the incidence of blood spot which reduce the internal egg quality , water quality may influence egg shell quality , water containing high level of electrolyte (saline drinking water) may have negative effect on egg shell quality and the water supplied to bird must also be hyagenic to ensure that disease is not transmitted by this route , the temperature of water provided for laying hen also is important especially during hot weather . it appear that hen reduce water intake or may cease to drink if the water gets too hot . studies have shown that provision of cool drinking water can improve egg shell quality in heat stressed hens

Diets containing high level of non starch poly saccharides increase gut viscosity , hold large amount of water and cause watery and sticky droppings 

Feed enzymes have been added to the diets of laying hens mainly in attempt to reduce the incidence of wet droppings and consequent management problems

Contamination of the feed with mycotoxins has the potential to reduce production and egg shell quality 

• stress 

1.general stress

wide range of general stress can affect egg shell quality , high population densities were shown some time ago to increase the production of body checked egg , body checked egg are thought to result from contraction of shell gland while the egg shell is in early stage of formation 
stress also can  induce delay in timing of ovi position  when egg retain their eggs and this can result in an increase incidence of white banded and slab sided egg

The stressor of relocation or exclusion from nest boxes of bird that normaly had access to them can cause an increase in the incidence of calcium “dusted”, white banded , slab sided and miss shaped egg 
even handling of birds which are not used to handling can increase the incidence of cracked eggs

 2.Heat stress
High temperature in some countries during summer can result in smaller eggs and reduced shell quality
heat stress reduce feed intake and limits the availability of blood calcium for egg shell formation . it may reduce the activity of carbonic anhydrase , an enzyme which results in the formation of bicarbonate which contribute the carbonate to the egg shell
sodium bicarbonate supplementation during heat stress may improve egg shell quality 
diets need to be formulated to match feed consumption and it should be recognized that bird eat most during the cooler times of the day. The addition of fat to the diet during hot weather has beneficial effects
the form of calcium provided affect the ability of the bird to produce good quality egg shell
the phosphorus requirement of laying hen increases slightly at hot weather
the provision of cool drinking water can reduce the effect of heat stress

• Disease

A number of trematode can inflame the oviduct that resulting in the formation of eggs with soft shell or shell-less
any disease that compromise the health of the bird may result in defective eggs and egg shells by indirect ways
some disease that affect the egg quality : Egg drop syndrome (EDS) , infectious bronchitis (IB) , new castle disease (ND) , infectious laryngotrachitis (ILT) 

Any pathogenic agent that grows in the tissue of reproductive tract can cause problems with egg shell formation 
infectious bronchitis : has been reported that cause egg shell to be pale in colour and sometime wrinkled appearance 
egg drop syndrome : cause drop in egg production and may also result in pale colour egg or rough shells
other diseases may cause production drops are Newcastle disease , Avian influenza , Avian encephalomyelitis and Mycoplasma gallisepticum (MG)

• Housing system 

The type of production system may influence the egg shell quality, early problem with cracked eggs in furnished cages have been greatly improved by changes in design of furnished cages to include egg saver wires
some problems of egg shell quality reported from free range systems , may result from inabililty to insure a balanced diet for the hens
some studies have found the effect of cage density on egg shell quality
cage free system produce eggs had greatest whipping capacity and foam consistency along with the lowest hough unit
cage produced eggs had lowest whipping capacity 

• Proprietary product

Some trace minerals are necessary in small quantities as : zinc , manganese which act as cofactor or activator for enzymes that involved in egg shell formation
proprietary products are available that provide the mineral in forms which improve their availability to the bird 

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Internal egg quality

The interior of hen`s egg consist of the yolk and albumen. A good quality egg should be free from internal blemishes such as blood spots , pigment spots, and meat spots

Albumen quality

Egg albumen has about 12% protein which the main ones are ovoalbumin 54%, ovo transferrin 13%, ovomecoid 11% and ovomucin 1.5-3% and lysozyme 3.5% 
factor affecting of the egg white 

• Age and storage of the egg : as the egg ages and carbon dioxide is lost through the shell , the content of the egg become more alkaline causing the albumen to become transperant and increasingly watery 
  at higher temperatures loses of CO2 is faster and the albumen quality deteriorates faster
  decreasing shed temperatures in hot monthes , combined with regular collection of eggs will help to reduce deterioration of albumen before collection
• Age of hen : hough unit will decrease with increase the bird age value 
• Consistency : albumin quality is measured in term of haugh units calculated from the height of the albumen and the weight of egg , a minimum measurement in HU for egg reaching the consumer is 60 , most eggs leaving the farm should be between 75-80 HU 
  albumen consistency influenced by:
• Nutrition :
  there are report of albumin quality decreasing by increasing dietary protein and amino acid content
  and increasing with increased dietary lysine concentration , ascorbic acid supplementation , vitamin E supplementation especially at high temperature .
• Contaminant :
  ingestion of crude oil result in lower Hough unit , vanadium also reduce albumin quality .
• Disease: the main disease of laying hen that has been reported to affect albumen quality is infectious bronchitis virus .

Yolk quality

Yolk colour :  egg yolk quality determined by the colour , texture , firmness and smell of the yolk , the yolk colour is the key factor in any consumer survey . the primary determinant of yolk colour is the xanthophyll content of the diet consumed 
its possible to manipulate the yolk colour of egg by addition of natural or synthetic xanthophyll to layer hen feed

Motted yolk : (many pale spots and blotches which vary in colour , size , shape) this case occur when the content of albumen and yolk mix as the result of degeneration and increase permeability of the vitelline membrane , dietary factors which may cause mottled yolks include :

• Some Anticoccidial agent
• Dewarming drugs such as piperazine
• Some antioxidants such as gallic acid and tannic acid

Yolk firmness : the yolk of fresh laid egg is round and firm , however as the egg ages and the vitelline membrane  degenerates , water from the albumen moves into the yolk and gives the yolk a flattened shape

Yolk texture : rubbery yolks may be caused by severe chilling or freezing of intact eggs

Blood and meat spots : blood spot occur when small blood vessels in the ovary rapture when the yolk is released 
vitamin k play an important role in blood clotting , vitamin k deficiency can result in increased occurrence of blood spots
avian encephalomyelitis has been reported as a cause of blood spots
mycotoxins may reduce vitamin k absorption and this may explain the elevated incidence of blood spots
meat spots  these are usually associated with the albumin rather than the yolk
blood spots increase with age of the bird and is reported to be higher in brown egg layer

Some Egg shell quality defects

• Pale-shelled Eggs

The degree of brown colour in the egg shell is dependent on the quality of pigment in the cuticle deposited onto the shell

Causes

• Bird age: higher incidence in older hens
• High stress in the flock
• disease: as Egg Drop Syndrome , Infectious bronchitis
• Use of chemotherapeutic agents, e.g. sulfonamides and nicarbazine

 

• Pink Eggs

The egg appears to be a pink or lilac colour because of the association between the cuticle and an extra calcium layer

Causes

• Stress
• Excess calcium in the feed

 

• Dirty Eggs

All or part of the egg shell is stained by faeces. Feed ingredients which can cause wet and sticky droppings should be avoided

Causes

• Wet-droppings
• High indigestible compound in feed
• Poor gut health
• Electrolyte imbalance/ saline water

 

• Blood Stained Eggs

Smears of blood are more common on eggs from pullets in early lay. These eggs become contaminated by blood from a prolapsed cloaca, cannibalism or vent pecking

 Causes

• Pullets are over-weight or coming into lay
• Sudden large increases in day length
• Poor hygiene in cage, trays and belt pick-up system

 

• Shell-less Eggs

The eggs are laid without a shell layer and are only protected by the shell membrane

Causes

• Immature shell gland
• Disease: Newcastle disease, infectious bronchitis, avian influenza, Egg Drop Syndrome.
• Inadequate nutrition: calcium, phosphorus, manganese or vitamin D

 

• Soft-shelled Eggs

These are eggs that are laid with an incomplete shell. A thin layer of calcium is deposited on the shell membrane

Causes

•  Excess phosphorus consumption
• Heat stress
• Bird age: higher incidence in older hens
• Saline water
• Mycotoxins

 

• Corrugated Eggs 

These eggs are characterised by a very rough and corrugated surface. These are thought to be produced when there is an inability to control and terminate plumping

Causes

• Inherited
• Newcastle disease or infectious bronchitis
• Excessive use of antibiotics
• Excess calcium consumption
• Copper deficiency

 

• Wrinkled Eggs 

Wrinkled eggs have thinly creased and wrinkled surfaces

 Causes

• Stress
• Disease e.g. Infectious brochitis
• Defective shell gland
• Over-crowding

 

• Pimpled Eggs 

Small lumps of calcified material appear on the egg shell. The severity of pimples depends on the foreign material present during the calcification process

Causes

• Bird age
• Strain of bird
• Inadequate nutrition

 

• Misshapen Eggs

A misshapen egg is an egg that differs from the normal shape and size is too small or large, round instead of oval or has major changes in the shape

Causes

• Immature shell gland
• Disease: Newcastle disease, infectious bronchitis, laryngotracheitis, Egg Drop syndrome.
• Defective shell gland

 

• White Banded Eggs 

These eggs are the result of two eggs coming in contact with each other in the shell gland pouch. At this point, normal calcification is interrupted and the first egg retained in the pouch will have an extra layer of calcium - seen as the white band marking

Causes

• Stress
• Changes in lighting

 

• Slab-sided Eggs 

The slab-sided egg is the second egg that enters the pouch. The second egg is not as complete as the first egg and is flattened at the point where the eggs made contact

Causes

• Stress
• Changes in lighting
• Disease

 

• Calcium Coated Eggs 

These type of eggs have an extra layer of calcium all over the egg or on just one end of the egg

Causes

• Defective shell gland
• Disturbances during calcification
• Poor nutrition, e.g. excess calcium.

 

• Hairline cracks

very fine cracks, usually run lengthwise along the shell. As they are difficult to detect, candling efficiency needs to be maximised . Their presence in fresh eggs can be revealed by carefull squeezing or tapping. The crack becomes more obvious as the egg ages
The incidence of this problem varies with flock age, but is usually 1 to 3% of total production

Cause 

• Ageing
• Poor nutrition
• Saline water
• Diseases such as infectious bronchitis
• High shed temperatures
• Mechanical damage caused by birds’ beaks and toenails
• Infrequent egg collection
• Rough handling
  
  
  
•  Star cracks

Star cracks are fine cracks radiating outwards from a central point of impact, which is often slightly indented

The incidence varies with flock age but is usually 1 to 2% of total production

•  Sandpaper or rough shells

The terms ‘sandpaper shells’ and ‘rough shells’ refer to eggs with rough-textured areas, often unevenly distributed over the shell

The incidence is normally less than 1% of total production, but may be higher for some strains of bird. It is also higher in early lay, often as a result of double ovulation, which produces one shell-less egg and another one with extra shell deposits

Causes 

• Diseases, e.g. infectious bronchitis, infectious laryngotracheitis or avian encephalomyelitis
• Defective shell gland Disturbances at the time a hen is due to lay can cause the egg to be held over for another day
• Incorrect or changes in lighting programme
• Water shortages
  
  
  
•   Blood spots

Blood spots vary from barely distinguishable spots on the surface of the yolk to heavy blood contamination throughout the yolk. Occasionally blood may be diffused through the albumen or white of the egg

The incidence varies between strains of bird and can be as high as 10%. Between 2 and 4% of all eggs contain some blood

Cause
Blood vessels rupturing in the ovary or oviduct, affected by:

• Levels of vitamin A and vitamin K in the diet
• Vitamin K antagonists (e.g. the drug sulphaquinoxaline and a component of lucerne meal)
• Fungal toxins
• Lighting programme
• Avian encephalomyelitis

 

• Meat spots

Most meat spots are pieces of tissue from body organs, but some may be partially broken-down blood spots. They are usually brown in colour, and found in the thick albumen, chalazae, or the yolk. They range in size from 0.5 mm to more than 3 mm in diameter

The incidence of meat spots ranges from less than 3% to 30% or more. It varies with the strain of bird, increases with the age of bird and may be higher in brown eggs. Many meat spots are too small to be detected by candling, especially in brown eggs. Less than 1% of eggs are usually downgraded because of meat spots

Causes 

Ageing of bird

• Watery whites

When an egg broken onto a flat surface has a watery, spread-out white, this usually indicates that the egg is stale. 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 to 110; the lower the value, the staler the egg

A minimum Haugh unit measurement of 60 is desirable for whole eggs sold to the domestic consumer. Most eggs leaving the farm should average between 75 and 85 Haugh units

Cause

• Old eggs
• High storage temperature and low humidity
• Ageing of bird
• Diseases, e.g. infectious bronchitis and egg drop syndrome
• Fungal toxins
• Ammonia
• Rough handling
  
  
  
•  Pale yolks

The colour of the yolk is due to substances called carotenoids. The nutritional value of the egg is not affected by the yolk colour. The intensity of yolk colour may be measured against standards such as the DSM Yolk Colour Fan. Most egg marketing authorities require deep-yellow to orange-yellow yolk colours in the range 9 to 12 on the DSM Yolk Colour Fan. Yolks of more intense colour may be required for specifi c markets

Causes

• Deterioration of pigment concentrates
• Insufficient carotenoids in the feed
• Insufficient pigment in birds that are coming into lay
• Oxidising agents or pigment antagonists in the feed
• Inadequate mixing of feed
• Storage of feed in damp and/or hot conditions

• Discoloured whites

The normal, slightly yellow-green colour of egg white may darken to an objectionable yellow or green, as shown, or may even become pink.

Causes 

• Excess of the vitamin riboflavin
• Ageing of the eggs and/or poor storage condition

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Control

• Follow an effective vaccination programme
• To avoid frightening birds, minimise human activity in and around the shed. Increase shed security to stop other birds and animals entering the shed
• Avoid overstocking
• There should not be sudden increases in day length as pullets come into lay, or lighting changes during lay
• Make sure that the water supply is adequate, that there are no blockages in water lines and that drinkers are functioning property
• Delay onset of sexual maturity 1 to 2 weeks by controlled feeding during rearing
• Make sure that birds’ nutrient intake is correct (particularly regarding calcium and vitamin D₃). Mixed feed should be handled carefully so that the different components do not separate out. This particularly needs to be checked when augers and automatic feeding systems are used
• Control temperatures by using foggers, fans, roof, sprinklers, white roofs, insulation and good ventilation
• Do not collect eggs in wire baskets. Reduce the severity of impacts during mechanical handling by:
  cushioning metal egg guides
  • keeping egg roll-out angles between 7 and 8°
  • minimising the number of rows of eggs being fedonto cross-conveyor belts at any one time
  • Educate staff to handle eggs with care during collection and packing
• The shed must be well ventilated
• Do not allow pullets to become over-fat, as the incidence of prolapse is greater in fat birds. There should not be sudden large increases in day length as pullets come into lay. Regularly clean cage bottoms and roll-out trays. Clean belt pick-up systems
• Keep nest boxes supplied with clean nesting material. Maintain proper hygiene, follow effective vaccination programmes and, when necessary, use appropriate medication to keep birds free of diseases which cause enteritis. Feed should not contain high levels of ingredients causing loose or sticky droppings, such as molasses and high-tannin sorghums
• Keep vitamin premixes cool and dry. If you prepare your own, they must be properly formulated and mixed
• Layer diets should not contain high levels of lucerne meal. Withdraw the drug sulphaquinoxaline from layers at least 10 days before collecting eggs for human consumption and follow any other requirements for correct medication