Factors affecting the Egg Shell Quality

Factors affecting the Egg Shell Quality

Muhammad Waqar

BS (Hons.) Poultry Science

Department of Poultry Production, University of Veterinary and Animal Sciences, Lahore

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The chicken egg is nature’s gift for mankind. An egg contains all essential nutrients such as proteins (all essential amino acids), fatty acids, vitamins, and minerals except Vitamin C in ample amount that it acts as a “Magic Capsule” for the consumer.

Quality:

The term “Quality” is very difficult to define. Everyone has its own likes and dislikes. A particular thing or character that is liked by one person may be unliked by the other. Therefore, in food items, when we talk about their quality, we must consider a broader perspective. A consumer may perceive quality through the appearance of the product, its packing or color and quality of packing material, food safety aspect of the product, and later its taste, smell, and after taste when we consume the food item.

Shell Quality:

Talking about shell quality, we can consider several factors as determining factors of the quality of the shell. It may be arguable that which factor is important from a consumer point of view and which is not, but all these factors may affect the internal quality of eggs and sometimes the development and quality of chicks produced in eggs. The quality of egg can be defined by the following parameters:

Shell Color

The color of the eggshell is the first parameter that influences the customer's decision to buy an egg. The shell of an egg can be white or different shades of brown. The color of the shell can be linked with the breed of the hen and it has no link with its nutritional value contrarily to the belief of many people.

Shell Cleanliness

The cleanliness of the shell can be defined as the outer appearance of the eggshell and the absence of any kind of fecal material, bloodstain, fly marks, and dirt. The cleanliness of the egg can be improved with management practices or installing an egg cleaning unit.

Shell thickness

The thickness of the eggshell is one of the most critical quality factors that can have many consequences. The inferior quality of eggshells can result in egg breakage, deterioration of the internal quality, lower hatchability, and poor chick quality. The optimum shell thickness is 0.34 mm but there are several factors that can affect this value.

Shell smoothness

The smoothness of the eggshell is another major factor that may affect the consumer's decision to purchase an egg. Although, it does not have any connection with the egg internal quality but still the appearance of the egg matters for the consumer. The shell can have pimples, sandy texture, ridges, and another such outgrowing that are mainly due to calcium imbalance in the body or problems associated with the shell gland of the egg.

Shell cracks

The cracks on the eggshell can also be a major factor that deteriorates its quality and increases the chances of microbial infection of the egg. The cracks could be caused by poor management, poor handling, and poor shell quality. The cracks will also increase the moisture loss from the egg. The cracks can be categorized into easily visible gross cracks or invisible from naked eye cracks such as hairlines or star cracks.

Shell porosity

As we know eggshell has more than 7000 pores for the exchange of moisture and gases. However, poor calcium in feed or damage in the uterus of a hen can result in an increase in the number of pores of the egg and ultimately lower egg quality.

All these characters of shell quality can be affected by several nutritional and management factors. Some of which we will discuss.

1.????Strain:

Some strains have the ability to deposit the Calcium faster than the others, resulting in better eggshell quality. For example, dark brown eggs have high shell quality than light brown eggs.

2.????Types of housing:

The type of housing system also has a direct effect on eggshell quality. Incidence of cracked eggs has been noticed in enriched cages which are improved by making egg saver wires and long nest curtains. In open houses, eggshell quality and production reduce during extreme seasons due to stress on the bird and lower feed intake.

3.????Disease:

Some diseases in layers affect egg production and eggshell quality. In Infectious Bronchitis, the eggshell becomes soft, discoloration and wrinkling of an egg also appear. EDS virus can also affect the shell gland but in the case of ND or IB, the whole reproductive tract may be affected.

4.????Age of Bird:

As a bird gets older, eggshell thickness decrease due to the large size of an egg and a finite amount of calcium deposition. At older ages, the amount of Ca in bones becomes less. Absorption of calcium decreases to less than 50% of normal, after 40 weeks of age.

5.????Molting:

With increasing age, egg production and eggshell thickness decrease. Induced molting techniques can be used to revert these changes up to some extent. Molting will rejuvenate the birds and ultimately increase the shell quality, texture, and breaking strength in all strains.

6.????Calcium and phosphorus:

The eggshell contains about 2 grams of Calcium, an average 4-gram of calcium in the diet that is necessary for maintaining health, and a superior quality shell of the egg. About 50%-60% of calcium is derived from the diet for eggshell deposition. During 15 hours of eggshell formation, calcium movement across the shell gland reaches a rate of 100-150 mg/hr. This process takes calcium from two sources bones and diet. Normal blood calcium level is about 20 - 30 mg/dl with a normal layer diet of 3.5% calcium, while layers on a 2% calcium diet, 30- 40% of the calcium are derived from bone. Therefore it is important to give more calcium in the pre-lay diet. When the shell gland is inactive, calcium absorption from the intestine is about 40%, it becomes 72% when shell gland is active.

The eggshell contains about 20mg of phosphorus. A high level of P in the blood inhibits the Ca release from bone. A high level of Ca increases the PH of the gut which results from low absorption of P. Absorption of Ca & P is interrelated with each other. Therefore the proper ratio of calcium to phosphorus (Ca: P ratio) for growing birds is 1.5-2.0 Ca: 1.0P is given to birds. P is an integral part of acid-base balance. Therefore, any change in the amount of Ca & P has an effect on eggshell quality.

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7.????Vitamin D3:

Vitamin D3 metabolites (1, 25 dihydroxy D3) are essential in the absorption of calcium. It is synthesized in the liver and kidney, any damage to it causes the decline in calcium absorption.

8.????Particle size of calcium:

Chen and Coon in 1990 demonstrated that the characteristics of eggshells are improved as the particle size of calcium is improved. The particle sizes vary from 2- 4mm that is considered good for the eggshell quality. The reason is that the particle size less than 1mm passes out the gizzard and mix in intestinal chyme in the duodenum and make a buffer with bile salts and raises the intestinal PH therefore the calcium is unavailable from the particle. Therefore, the breeding companies recommended a mixture of course and fine particles of calcium.

9.????Environmental Temperature:

Higher Environmental temperature causes poor eggshell quality. When Environmental temperature increases, birds started panting which reduces the CO2 level in blood and causes Respiratory alkalosis which lowers the availability of Ca. The pH of the blood becomes alkaline. This disturbance in acid-base balance causes soft shell eggs in summer. At high ambient temperature (>27oC), feed consumption becomes low, therefore the shell thickness reduces temporarily. It became normal when the environmental temperature reduces and feed intake increases. Under heat stress, more blood flows towards the peripheral tissues and causes low blood flow towards the oviduct which results in lower eggshell quality.

10.?Stress:

Even good genes of better egg production and eggshell quality are also affected by environmental stresses. Egg Shell is formed by the activity of cells lying in the uterus and oviduct, under the stress the secretion of cells becomes acidic and even the cells may damage or be destroyed. In some cases, the deposition of more calcium is noticed that causes misshapen eggs. Relocation stress has a visual effect on eggshell quality. A major type of relocation is shifting the bird to a completely new house.

11.?Intestinal pH:

Absorption of P is optimal in 5.5-6.0 pH. But in greater pH than 6.5, the absorption of P is declining. More free fatty acids in the diet cause the pH to decrease and interfere with calcium and phosphorus absorption.

12.?Feed formulation:

Shell breaking strength is greater for the sorghum diet than wheat or barley-based diet. Higher levels of calcium and phytate in the diet reduce the availability of minerals, especially manganese and zinc. Anti-nutritional factors in diet affect the availability of nutrients e.g., Phytate in the diet reduces the availability of phosphorus. Thus, the addition of phytase enzyme in diet can improve the eggshell quality.

13.?Mycotoxins:

Aflatoxin attacks the liver and kidneys ultimately reducing vitamin D metabolism that reduces the ability of birds to absorb calcium from the diet and its movement to the shell gland and medullary bones. Zearalenone mycotoxin binds with calcium to form a complex in the intestines and reducing calcium availability.

14.?Effect of antibiotics:

Some drugs have an effect on eggshell quality. For example, sulfa drugs affect eggshell quality, but tetracycline has a beneficial effect on eggshell quality.

15.?Time of production:

The thickness of eggshell is determined by the Amount of time stay of egg in uterus rate of deposition of Ca in the shell. The time of day when the egg is laid determines the eggshell quality. The eggshell will be thick when laid in an early day or light photoperiod.

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