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DR.S.P. KALASKAR

BVSC & AH, MVSC (Nutrition)

Nutritionist

Vetrix Nutrition Pvt Ltd.

(09890942732)

Maintaining Egg Shell Quality

The egg is highly complexed reproductive cell, as yolk is surrounded by albumen, this entire mass is surrounded by two membranes and an external covering we called it egg shell. The shell provides a proper shape to the egg and is meant for conserving the valuable nutrients within the egg. Hen egg contains approximately 77% water,12.2% protein,10.4% lipids and rest vitamins, minerals and carbohydrates.

Egg Shell:

The outer cover of the egg, the shell comprises 9-10 % of total egg weight. On an average the eggshell weighs 4-5g, with remarkable mechanical properties of breaking strength and is 300-350 micrometer thick. The calcium content of the eggshell is approximately

1.7-2.6g.

Composition of Egg Shell:

vCalcium carbonate: 94-96%

vPhosphorus: 0.31%

vMagnesium: 0.22%

vSodium, Potassium, Manganese, Iron and Copper: traces

vOrganic matter: <2%

Shell Quality:

For commercial layer and breeder operations, shell quality means increased

shell thickness and shell breaking strength to reduce number of cracked eggs, and increased number of saleable / hatching eggs.

Methods to Measure Shell Quality:

Egg shell quality can be measured as:

vEgg size and visual shell defects

vSpecific gravity

vShell color

vShell breaking strength

vPercentage shell (Shell weight X 100/Egg weight)

vShell thickness (mm)

Specific Gravity:

The specific gravity of an object equals the weight of its volume relative to the weight of an equal volume of water, (when both are at the same temperature.) The specific gravity of an egg is equal to the egg’s density relative to water.

The specific gravity of all four parts of the egg is different

Shell: 2.324,

Yolk: 1.031,

Albumen: 1.037,

Shell membranes: 1.074.

Since the specific gravity of shell is more than two times higher than the other parts of the egg, the percentage of the shell has major influence on the specific gravity of whole egg. As the amount of shell increases, the specific gravity of the egg increases, Egg specific gravity, therefore, is a good indicator of percentage shell and shell quality. The incidence of breakage is above normal, if the specific gravity of a flock averages less than 1.077.

Shell Quality Defects:

These defects are obvious from external observation / candling and are important for evaluation for the producer and consumer. These may be as:

( A ) Mis-shaped Eggs:

If albumen quality is very poor and there is no sound foundation upon which to build the true shell, the shell may break in the shell gland during the formation process.

Mis-shaped eggs are due to any factor which causes disturbance to the birds

10-13 hours before the egg is laid is likely to increase the incidence of this fault.

B) Coated Shell

Any stress or disturbances at the time egg is due to be laid will encourage the bird to retain the egg, typically these faults are caused by the egg remaining in the shell gland for an extended period. Often young flocks just coming into production are very susceptible to this defect.

(C) Rough Shelled Eggs

In some cases, two eggs may be in the shell gland at the same time which can cause a form of rough shelled egg.

(D) Soft & Weak Shelled Eggs : Soft and weak shelled eggs can be common in older birds especially those which are nearing the end of the laying period. If an egg is retained in the shell gland for too long, the next ovulation takes place at the usual time but before the previous egg is laid , So the second egg may spend less time then normal in the shell gland and the result is a soft or shell-less egg.

Cracked Eggs:

Egg shells can easily be damaged after the egg is laid and cracking is one of the most common reasons for downgrading, It may be due to an inadequate egg shell being

laid or to poor handling which may occur during collection, grading or transportation.

Three main types of cracks are identified.

Hairline Crack :

Hairline Cracks are the most difficult to identify, particularly in very fresh eggs.

Hairline cracks are often caused by an egg colliding with an inflexible surface.

Star Crack:

May often be visible under normal light although they are more easily seen during candling. A central point of impact may be seen and it may often due to collisions between eggs.

Pin-hole &Toe-hole Crack :

Can be caused either by the birds themselves or by any sharp protrusions which may come into contact with the egg.

Dirty & Glazed Shells:

After the egg is laid, it can become affected with numerous contaminants, all of these lead to eggs being downgraded. High standards of hygiene and management and pest

control bust be maintained to overcome this defect.

Factors Influencing Shell Quality:

Thickness:

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.

Diseases:

Diseases like infectious bronchitis (IB), Newcastle disease (ND),Avian influenza (AI) and

Egg Drop Syndrome (EDS) affect shell gland. EDS Virus affects only the shell gland but with ND or IB, every portion of the reproductive tract can be affected virus causes soft/rough shelled eggs, discoloration and wrinkling of the shell.

Management:

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.

Age of Birds:

As the hen ages, the thickness of the shell usually declines. Older Flocks lay larger eggs, which break easily. (The hen is genetically capable of placing only a finite amount of calcium in the shell.) Hen loses some of 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 50 weeks of age.

Water Quality:

Many studies showed that saline drinking water, including tap water, underground bore water containing sodium chloride, has an adverse effect on eggshell quality, while having very little effect on feed intake, egg production or egg weight.

Stress:

The shell is formed by the activity of cells lying 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 and results in misshaped eggs.

Environmental Temperature:

During exposure to high temperature, the hen reacts by increasing its rate of breathing (panting) in order to cool itself. This causes the lowering of CO2 in the blood.  (“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.

Nutrition:

There is a complex relationship between calcium, phosphorus, vitamin D3 and the hormonal system of the layer in calcium metabolism during lay. 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 3.8 – 4.0% calcium,0.38 – 0.44% phosphorus)

Calcium:

Both excess and deficiency of calcium will negatively affect the egg shell quality. An egg contains almost 2 grams calcium; hence an average of 4 grams of calcium intake per day is required by a layer to maintain good shell quality. (since only 50-60% of dietary calcium is actually used in shell formation.)

During the last 15 hours of shell formation, calcium movement across the shell gland reaches a rate of 100-150 mg/hr. This process draws calcium from two sources: diet and bone. Normal blood calcium level is about 20-30 mg with a normal layer ration of 3.56% calcium or higher, while layers on a 2% calcium diet ,30-40 % of the Calcium is

derived from the bone. It is therefore important to have pullets, prior to lay, on a high

level of calcium to store it on body.

when the shell gland is inactive Intestinal absorption of calcium in the diet is about 40%, 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 from bone. Large particle sizes of calcium sources allow calcium to be metered throughout this time.

Phosphorus

The phosphorus content of the eggshell is small i.e. 20mg compared with 120mg in the egg contents. There is also uneven distribution of the phosphorus in the inner

and outer layers of the shell. High levels of phosphorus in the blood will inhibit the

mobilization of calcium from bone. The absorption of calcium and phosphorus are interrelated and can be influenced by…. Source and form of Ca and ph. Calcium source and particle size plays a role in calcium level in the gut when needed.

Intestinal pH: Phosphorus absorption is optimal at pH 5.5-6.0. When the pH is higher than 6.5, absorption of phosphorus markedly decreases.

Ca and Ph ratio: High calcium of phosphorus levels in the intestine reduce the absorption of both.

High calcium increases the pH in the gut and phosphorus absorption is decreased along with zinc and manganese

Vitamin D3 is vital for absorption and mobilization of calcium during shell synthesis.

Vitamin D3 is the major control element in stimulating calcium absorption from the intestine.

How to Improve Shell Quality?

Vitamin C (Ascorbic Acid) is essential for synthesis of organic matrix (tropocollagen) of eggshell. Ascorbic acid alleviates the ill effects of heat stress by reducing the plasma cortisone level in the bird. Ascorbic acid is a co-factor in the conversion of Vitamin D to

the active hormonal metabolite “Calcitriol” (1.25 (OH)2D3) which stimulates intestinal absorption of calcium and thus elevates plasma calcium to a level that supports normal mineralization of bones. A dietary level of 250 mg ascorbic acid/Kg diet improves the

egg production and eggshell quality by enhancing intestinal calcium absorption.

Sodium Bi Carbonate (NaHCO3) Supplementation of NaHCO3 to laying hens at high temperatures is a means of improving eggshell quality. (as hens consume the additional

bicarbonate during the period of active shell formation.) The addition of sodium bicarbonate has shown to elevate the dietary electrolyte balance, improved acid-base balance and has a positive effect on eggshell quality.

Minerals: Zinc, Manganese and copper are compounds involved in the metabolic process of eggshell formation. These trace minerals work as co-factors of enzymes involved with shell matrix formation.

Calcium: Provide extra calcium to the older hens @ 1 g/bird in the form of shell or stone Grit (over and above normal requirement in summer. ) Maintain the desired particle size of calcium source. The minimum size of calcium source to improve gizzard retention is about 1 mm. Magnesium content of calcium source must be as low as possible.

Management: Reducing egg breakage at farms requires constant attention to management details and proper equipment maintenance. Some methods to reduce

the percentage of broken eggs are:

1)Provide cushioning at the front of egg collection area of the cages.

2)Collect the eggs at least twice a day and more often if possible.

3)Maintain egg collection wires/trays in good condition.

4)Ensure that eggs do not pile up.

5)Routinely check the quality and condition of the egg trays.

6)Train Egg collection workers for carefully picking the eggs from the cage area. (gently placing them in the collection trays without slowing down the collection process.)

6)Procure good quality feed ingredients without contaminants and mycotoxins and provide wholesome water at all times to the birds.

Maintaining eggshell quality is a far more complex activity. We can however make significant reductions in the number of eggs lost due to poor shell quality. This can be achieved if we realize that no single factor is responsible for egg breaking. Many factors are known to be co-related with eggshell quality including flock health problems, management practices, environmental conditions and adequacy of nutrition.