How to improve Eggshell quality in Commercial Layers


Poor egg shell quality is a significant problem in the poultry industry, negatively affecting the economic results of egg production, as well as decreasing the hatchability of eggs and increasing embryonic mortality. Protection of the embryo from the harmful influence of outside environmental factors, regulation of gas and water exchange and serving as a Ca supply for embryonic development are the main functions of the egg shell. Incidence of inferior shell quality still remains as one of the major causes of economic losses to egg producers throughout the world. 

The breakup of this may be 1.0 to 3.0 per cent in collection, 2.0 to 3.0 per cent in packing and 2.0 to 4.0 per cent during transportation and trade channels. The highest rate (1.07 per cent) of egg breakage was noticed among the age group of 61-80 weeks and the lowest rate (0.48 per cent) of egg breakage was noticed among the age group of 20-40 weeks. The incidences of eggshell breakages in commercial layer farms were increasing as age advances. It may be due to insufficient mobilization of calcium from bones for eggshell formation et al.2 . Since, the proportion of cracked eggs increases with the age of the bird, it is especially important to reduce egg breakage during later part of the production period.

How to improve Egg Shell quality in Layers
How to improve Egg Shell quality in Layers

Egg shell quality is also an important concern for consumers, as strong resistance to breaking and lack of shell defects are essential for protection against the penetration of pathogenic bacteria in to eggs. This is an especially crucial problem in the European Union, where scale of egg production in cage systems is being gradually reduced. It was well demonstrated by several researchers that total microbial load of egg shells is lower for cage system eggs compared with free-range. Many factors affect egg shell mineralization and quality, including genetic, environmental and nutritional factors, as well as the health status of hens. Most studies on dietary effects on egg shell and bone quality in laying hens have focused on macro minerals and Vitamin D3. However the results of some recent experiments have demonstrated that certain dietary levels and sources of certain micro elements, mainly Zinc and Manganese as well as diet supplementation with certain feed additives influencing the metabolic indices of the gastro intestinal tract can beneficially affect the egg shell mineralization process and egg shell quality.


The fertile egg is highly complexed reproductive cell and is a tiny center of life, where initial development of embryo takes place. Most of the commercial eggs are infertile. The yolk is surrounded by albumen, having high water content, elasticity and shock absorbing capacity. This entire mass is surrounded by two membranes and an external covering called 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 76% water, 12% protein, 10% lipids and rest vitamins, minerals and carbohydrates. Egg is a major source of human dietary protein with high biological value and excellent protein efficiency ratio.

Egg Shell:

The outer cover of the egg, the shell comprises 10-11% of total egg weight. On an average the eggshell weighs 5-6g, with remarkable mechanical properties of breaking strength and is 300-350 micrometer thick. This structure plays a crucial role in protecting the contents of the egg from the microbial and physical environment and in controlling the exchange of water and gases. The calcium content of the eggshell is approximately 1.7- 2.5g. An average eggshell contains: 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. There are about 8000 microscopic pores on the shell. The outer surface of the shell itself consists of a mucous coating (cuticle) which is deposited on the egg just prior to the lay. This proteinous covering helps to protect the interior content of the egg from bacterial penetration through the egg shell.

Shell Quality:

The aesthetic quality of the egg shell relates to the quality factors which one can observe; such as soundness of the shell, shape of the shell and colour of the shell. However, for commercial layer and breeder operations, shell quality means increased shell thickness and shell breaking strength to reduce number of cracked eggs, an increased number of saleable/ hatching eggs and a higher number of viable day old chicks. Diet formulation: Shell breaking strength was greater for the sorghum diet than wheat or barley based diet and less for maize-soya diet. High levels of calcium and phytate in the diet of laying hen reduce the availability of trace minerals, especially manganese and zinc. Addition of non starch polysaccharides and phytase enzymes to the feed tends to improve eggshell quality. No deleterious effects on egg and eggshell quality were observed when levels of chloride and magnesium were up to three times higher than recommended levels. Excess dietary chlorine, however, decreases blood bicarbonate concentration, which plays a pivotal role in eggshell calcification. Low dietary cationic-anionic balance, presence of non starch polysaccharides, mycotoxins and contaminants results in poor shell quality.

Eggshell quality is of major importance to the egg industry and also has a major economic impact on commercial egg production. Broken and cracked eggs represent an economic loss to egg producers. Some 6-8% of all eggs produced commercially are unusable because of poor shell quality. Numerous factors involved in eggshell quality include nutrition, age, stress and disease.

Achieving the proper pullet body weight is the first step in maintaining good early egg size
Underweight pullets are one of the most common causes for small early eggs. It is known that underweight pullets produce more small eggs early in the production cycle. For every additional 45 grams in body weight at 18 weeks of age, the egg size increases 0.5 grams. In addition, underweight pullets usually do not have the skeletal frame necessary to maintain good egg shell quality after 40 weeks of age. Underweight pullets tend to be underweight as layers. The pullet body weight is affected by nutrition, disease, lighting, space allotment and beak trimming.

It is important to weigh pullets regularly to monitor their growth. A good weight monitoring program begins at four weeks and every two weeks thereafter, 100 pullets are weighed. Cages should be selected representing different locations within the pullet house. All birds in the cage should be weighed. Weighing the same cages increases the accuracy of the information. The weights of birds on the return side of the feeder line should be compared with the supply side to ensure that pullets are being fed frequently enough. By weighing every two weeks it is easier to identify the factors responsible for slowed growth. Weighing should coincide with changes in feed. If flocks are not at the target body weight for their age, the feed change should be delayed to give the underweight birds a chance to catch up. The variability of the body weights is as important as the average body weight. The goal for uniformity is that 90% of the birds should be within 10% of the average body weight.
A pullet will grow at its maximum rate between 9 and 14 weeks of age. This is the time at which the skeletal structure of the bird reaches its adult size and the oviduct matures and prepares for the onset of egg production. Stressful events during this time can have profound effects on body weight gain. If possible, stressful management practices such as moving or handling birds for vaccinations or beak trimming should be avoided during this period. Beak trimming is best completed prior to six weeks of age. The most appropriate time for the first beak trimming is seven to ten days of age, with the second beak trimming, if necessary, done at six weeks. Birds will recover more quickly and suffer less growth suppression from an early beak trimming.

Moving pullets into the laying unit late (18 or 19 weeks of age) can be harmful because pullets may become overcrowded for the final two weeks prior to moving. This can result in restricted feed and water consumption for some birds. Late overcrowding of pullets can be avoided by moving at 15 to 17 weeks of age.

Lighting programs to achieve good early egg size

One way to improve pullet body weights at the onset of egg production is to delay sexual maturity. Genetic selection has been advancing the rate of sexual maturity by about one day per year. Early maturity can be a valuable trait, provided the necessary body weight has been attained. However, if at least the standard body weight is not present at 18 weeks, the light stimulation of the flock should be delayed until the standard body weight is attained. Larger early egg weight is often the result of birds being heavier at sexual maturity. 

Encouraging more feed consumption early in the laying period will also promote larger early egg size. Management practices such as increasing the frequency of feeding or lowering house temperature can increase feed consumption. Sexual maturity can be delayed by using a lighting program that “steps down” the amount of light given to the pullet flock during the growing period after nine weeks. An example of a step down lighting program designed to delay sexual maturity is shown below:

Step Down Program #1

Step down lighting Program #2 is an alternative approach. In this program, the hours of light decrease gradually during the first ten weeks of age and are then held constant until 18 weeks. This program will have no effect on sexual maturity, because the step down in the amount of light is stopped by ten weeks, which is the time when pullets become sensitive to light. This program promotes better growth in pullets by allowing more feed consumption because of the additional hours of light provided to the young pullets.

Energy intake and egg size

It is generally assumed that the feed intake of laying hens will vary with the energy content of the feed. In other words, higher energy rations result in lower feed intake. While this usually does occur, the expected decline in feed intake is seldom fully achieved. The result is a net increase in energy intake for the hen. Feeds formulated with low energy ingredients such as wheat and barley often result in insufficient energy intake for hens to maintain good production (<2800 Kcal/kg). It may not be physically possible for these hens to consume enough feed to meet their energy needs, especially during the time of peak production. In such situations, egg size will be the first production trait to suffer. The decrease in egg size is a result of dietary and body proteins having to be utilized for energy, precluding their use for egg mass formation.

Required nutrient intake per bird per day Peaking

(50% production to 32 weeks), 32-44 Weeks, 44-58 Weeks, 58 Weeks onwards

Protein (g) 16.25 15.75-16.25 15.25-15.75 14.75-15.25
Methionine (mg) 360 360 350 340
Methionine + cystine (mg) 670 660 620 580
Calcium (g) 3.65 3.80 3.90 3.90
Phosphorus available (g) 0.47 0.45 0.40 0.30
Phosphorus total (g) 0.67 0.65 0.55 0.45

Phase feeding helps maintain egg shell quality throughout the laying period

Nutritional requirements change for a laying hen as it proceeds through the production cycle. The requirements of a hen during peak egg production differ greatly from her requirements later in the production cycle. The feed intake also increases between 18 and 35 weeks of age, affecting the nutrient density needed in the feed to satisfy requirements. Phase feeding is the best method of meeting these changing nutrient requirements. Phase feeding prevents overfeeding of nutrients, which unnecessarily increases feed costs. The production cycle is generally divided into pre-lay, pre-peak, peaking and post peaking phases. In order to maintain the eggshell quality in older hens, the amount of dietary calcium must be increased at each phase. An increase in dietary calcium is needed because the older hen is less efficient at absorbing calcium from the diet. To facilitate better calcium absorption, hens over 40 weeks of age should be fed a calcium source of a large particle size.

Phase feeding can prevent older hens from developing an excessively large egg size by not allowing hens to over consume sulfur-containing amino acids (methionine and cystine) and phosphorus. Keeping the egg size below 63 grams is critical to maintain good eggshell quality in white egg varieties. Chickens usually deposit the same amount of shell on eggs regardless of their size, therefore, larger eggs are prone to having thinner shells and will be more likely to crack. The egg size can be maintained through phase adjustments in the feed formulation. Reductions in the amount of dietary protein, available phosphorus and methionine help maintain egg size at a point at which good shell thickness can be sustained.

But the most important factor which should be managed for the bird’s health and to maintain good eggshell quality is heat stress.

Effect of heat stress

The extent of heat stress will be influenced by factors such as humidity and the extent to which the birds have become acclimatized. The deleterious effects of heat stress on eggshell quality appear to be due to several reasons. Both heat exposure and reduced appetite affect the laying performance and eggshell quality of birds exposed to high ambient temperatures. Whereas egg production and egg weight are influenced to a major extent by the reduction in feed consumption, eggshell quality is influenced primarily by high temperature.

• Heat stress in birds causes many biochemical and physiological changes, such as shifts in acid-base balance, hyperthermia, increased oxygen consumption and the release of carbon di-oxide, increased production of free radicals and corticosterone.

• Depressed feed intake results in decreased calcium consumption.

• At high temperatures, birds pant to enhance evaporative cooling. Panting results in respiratory alkalosis, which is caused by loss of carbon dioxide from the blood and involves an increase in blood pH. This, in turn, decreases the proportion of the blood calcium that is in the ionized form and reduces the amount of calcium available for eggshell formation.

• The activity of carbonic anhydrase (the enzyme which produces bicarbonate for shell formation) is also reduced during heat stress and blood flow to the uterus is also decreased.

• Under high temperature, blood flow within the body is changed and more blood flows to peripheral tissues to transfer more heat from the body core to the surface. The decreased concentration of plasma calcium and the partial pressure of carbon dioxide is attributable to respiratory alkalosis.

• Reduction in shell weight.

• Low shell thickness.

• High eggshell reflectivity. The light colored shell of the eggs laid during heat stress is due to the reduction in pigment deposited in the cuticle.

Bicarbonate supplementation

Loss of carbon dioxide is accentuated by the need for blood bicarbonate to buffer the hydrogen ions produced during eggshell formation. A reduced bicarbonate concentration in the lumen of the shell gland adversely affects eggshell quality, leading to the laying of rough-shelled eggs. It is therefore possible that, at high temperatures, hens have a nutritional requirement for bicarbonate in order to improve eggshell quality by supplementing the diet with sodium bicarbonate at the rate of 2-2.5 kilogram (kg) per ton of feed.

The eggshell formation occurs normally during dark periods, but sodium bicarbonate intake by birds does not happen during dark periods. In order to improve sodium bicarbonate intake, the birds are provided with an extended photo period of 18 to 20 hours. An extended photo period does not affect egg production during heat-stressed conditions. Continuous lighting allows hens to consume the dietary supplements during the period of active eggshell formation. If sodium is increased by supplementation with sodium bicarbonate, then, to balance the higher level of sodium, ammonium chloride is supplemented along with the sodium bicarbonate at the ratio of (40:60).

Zinc supplementation

Carbonic anhydrase is reduced during high temperatures. Carbonic anhydrase is required to form bicarbonate that passes through the shell gland to form calcium carbonate. So zinc supplementation in the form of zinc methionine or zinc propionate increases the carbonic anhydrase activity that alleviates the effect of heat stress and maintains better eggshell quality.

Potassium Chloride supplementation

Water is an essential nutrient which facilitates the transfer of the minerals (Na+, K+, Cl-). The water intake during summer increases to three times the feed intake. The water circulation in the body system reduces body heat. In cases of heat stressed birds, the water intake becomes suppressed. So, along with the water, potassium chloride mixes at the rate of 0.5-0.6%, improves the water intake by 90%, increases evaporative heat loss by 80% and increases apparent respiratory efficiency by 25%.

Chromium and Manganese supplementation

Heat stress effects are counteracted by chromium (Cr) and manganese (Mn) supplementation in feed. The addition of 20 milligrams (mg) of Cr/kg and 120 mg of Mn/kg of diet alters eggshell thickness.

Ascorbic acid supplementation

Ascorbic acid is a natural supplement available to alleviate heat stress in layers during hot weather. Adding 5 milliliters of lemon juice per liter of drinking water will reduce eggs with broken and fragile shells. The useful effect of lemon juice on the eggshell quality of heat-stressed birds could be due to ingredients such as the ascorbic acid in lemon juice.

Although poultry can synthesize vitamin-C, its quantity becomes insufficient during heat stress as a result of its increased rate of usage to combat the free radicals generated. Vitamin C supplementation at 500 parts per million (ppm) is beneficial to maintaining bird performance, including interior and exterior egg quality under severe environmental stresses. The decline in eggshell quality is affected not only by the decreased intake of calcium and phosphorus, but also by the depletion of the ascorbic acid required for the conversion of 25-hydroxycholecalciferol-r into the one 25-dihydroxycholecalciferol produced in the kidneys, which is essential for regulating calcium metabolism and eggshell calcification.

Vitamin-E supplementation

In a normal bird, there is sufficient antioxidant capacity to remove active oxygen; but when exposed to environmental stress, this may be depressed. Through its intra-membrane antioxidant properties, vitamin E may protect tissue membranes from the lipid peroxidation caused by free radical attacks and it alleviates the effects of environmental stress in laying hens. Supplementation of vitamin C at 200 mg/kg and vitamin E at 250 mg/kg in the diet can ameliorate the detrimental effects of heat stress and improve the egg quality parameters of egg weight, eggshell weight, albumen and yolk weight.

Vaccination programs to enhance internal and external egg quality

It has been well documented that some infectious diseases can have an adverse effect on egg quantity and quality. Any infectious process eliciting an inflammatory response could affect egg production through an effect on feed and water intake. In addition, there is a repartitioning of amino acids and proteins away from productive activities, such as egg production, towards the more immediate need for antibody production and other components of the immune response. Newcastle disease and infectious bronchitis are known to cause drops in egg production and the formation of weak and defective eggshells because of direct damage to the oviduct. There are many successful approaches towards Newcastle and bronchitis vaccination. The strains of vaccine used and the routes of administration depend on the degree of risk for these diseases in an area.

It is important to establish good flock immunity during the growing period when the oviduct is developing and to develop a strong immunity prior to the stress of egg production. Typically the greatest challenge for bronchitis occurs after the birds are housed on the laying farm. In some situations, the pullet vaccinations are sufficient and there is no need for further vaccinations. On layer farms where a higher risk to Newcastle and bronchitis exists, there are two options for further vaccinations. One is to inject an inactivated Newcastle/bronchitis vaccine at the point of egg production (generally 14 to 16 weeks). The second option is to continue vaccinating with live vaccines through the egg production period. The interval for these live vaccinations are typically every six to ten weeks. There are advantages and disadvantages to either approach.

Mycoplasma monitoring 

Mycoplasma galli-septicum (MG) and Mycoplasma synoviae (MS) could play a role in problems of poor egg size and quality through the interaction with Newcastle, bronchitis and other respiratory pathogens. It has been clearly shown that the infection of the trachea with MG or MS can affect the severity of disease caused by other respiratory pathogens. MG and occasionally MS can directly effect egg production by ovarian infection. It is important to monitor for these pathogens. Breeding companies go to great lengths to ensure freedom of their stock from infection with MG and MS. It is common that commercial pullets are grown free of MG or MS and become infected after placement on infected multiple aged layer farms.

Monitoring for mycoplasma is done by submitting 25 samples per flock monthly for testing with the plate agglutination antigens.

The options for infected flocks are either vaccination or medication. Both can be beneficial in reducing the effects of infection and minimizing production losses but will not eradicate it from the flock. Both inactivated and live vaccines for MG are available. 

The newer live MG vaccines, 6/85 (Intervet) and TS-11 (Select), are effective and do not spread from bird to bird.

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