Eggshells are composed of around 95% calcium carbonate, a mineral that is very important for industry, nutrition and agriculture. There are many studies trying to find new ways to utilize this resource and their natural absorbent properties, as in treating cadmium in wastewater. So, never toss out those egg shells. They’re not garbage, but can be very useful around the house and yard. They also help to save you money by replacing many expensive, toxic chemical products you might have normally used otherwise. Most good quality eggshells from commercial layers contain approximately 2. 2 grams of calcium in the form of calcium carbonate.
About 95% of the dry eggshell is calcium carbonate weighing 5. 5 grams. The average eggshell contains about 0. 3% phosphorous, 0. 3% magnesium, and traces of sodium, potassium, zinc, manganese, iron and copper. If the calcium from the shell is removed, the organic matrix material is left behind. This organic material has calcium binding properties, and its organization during shell formation influences the strength of the shell. The organic material must be deposited so that the size and organization of the crystalline components (mostly calcium carbonate) are ideal, thus leading to a strong shell.
The majority of the true shell is composed of long columns of calcium carbonate. There are other zones that are involved in the self-organization giving the eggshell its strength properties. Thus, shell thickness is the main factor, but not the only factor, that determines strength. At present, dietary manipulation is the primary means of trying to correct eggshell quality problems. However, the shell to organic membrane relationship is also critical to good shell quality and must be considered. An eggshell that is smooth is desirable, as rough-shelled eggs fracture more easily. Large eggs will usually break more easily than small ones.
The main reason for this is that the hen is genetically capable of placing only a finite amount of calcium in the shell. As the hen ages and the eggs get bigger, a similar amount of calcium has to be spread over a larger surface. Therefore, controlling the rate of egg weight change can influence eggshell quality as the hen ages. Controlling feed intake by changing the temperature inside the layer house influences egg size. It must be remembered that many factors can influence the amount of calcium being laid down by the hen. Just because an eggshell is thick does not necessarily mean that it is strong.
Sometimes a thinner eggshell is stronger than a thicker eggshell. The reason for this is due to the shape and organization of the organic and inorganic components of the shell. Usually, eggshell quality is not as much of a problem in cooler environments as it is in hot environments. One of the contributing factors causing poorer eggshell quality in hot weather is hens not consuming adequate feed. This can lead to problems in body weight, egg production, egg size, and eggshell quality if measures are not taken to assure adequate daily nutrient and energy consumption.
When environmental temperature becomes excessively hot, feed intake decreases, and energy becomes the first limiting factor to the hen. Inadequate consumption of amino acids, calcium, phosphorus, and other nutrients can usually be corrected by adjusting the nutrient density of the diet. However, it must not be forgotten that in hot weather, unlike cooler weather, the laying hen has to make critical life sustaining physiological adjustments in order to cope with the increased environmental temperature. The laying hen, through panting, resists the rise in body temperature during periods of heat stress.
At the same time, the acid-base balance in the bird’s blood is changed. We sometimes forget that the laying hen has to cool her body in extremely hot environments and this will shift her physiological priorities from producing eggs and maintaining an adequately calcified eggshell to that of staying alive. In such situations, maximum egg mass (egg production times egg weight) along with maximum eggshell quality are difficult to achieve with any age bird. Not all diseases affecting chickens cause a decline in eggshell quality. However, egg production will usually decline.
An example of a disease that can affect the numbers of eggs and not necessarily the quality is infectious laryngotracheitis. Other common viral diseases, such as egg drop syndrome (EDS), avian influenza (AI), Newcastle disease (ND) and infectious bronchitis (IB), may produce severe effects on eggshell and internal quality. Many times the total number of eggs is not influenced, even though the egg records indicate a drop in total collectable eggs. This is due to the increase in non-collectable eggs (shell-less or ultra-thin shells) that are lost under the cages. This is a common occurrence with EDS.
It has been established that the EDS virus affects only the shell gland, but with ND and IB every portion of the reproductive tract can be affected. If one disease had to be singled out as being responsible for the majority of the economically significant production losses in egg layers, it would have to be infectious bronchitis. Infectious bronchitis virus, a coronavirus, has a preference for the mucus membranes of the respiratory and reproductive tracts. The kidney is also affected by certain IB virus strains. Not only is eggshell quality affected, but internal quality also declines.
Watery whites are very common and can persist for long periods after egg production returns. Also, an IB outbreak can result in a pale-colored shell in brown shell eggs. What is Egg Shell Quality and How to Preserve It There are many factors that affect the overall quality of the egg shell, but before discussing these factors, it is important to know what makes up the structure of the egg shell. The egg shell consists of about 94 to 97% calcium carbonate. The other three percent is organic matter and egg shell pigment. There are also as many as 8,000 microscopic pores in the shell itself.
The outer coating of the shell itself consists of a mucous coating called the cuticle or bloom which is deposited on the shell just prior to lay. This protein like covering helps protect the interior contents of the egg from bacteria penetration through the shell. Egg shell quality is determined by the color, shape, and structure of the shell. Colors can range from white to tints to brown and egg shape can also vary. Numerous factors affect the general functional quality of the egg shell. These factors affect the quality of the shell mostly prior to when the egg is laid.
The thickness of an egg shell is determined by the amount of time it spends in the shell gland (uterus) and the rate of calcium deposition during egg shell formation. If the egg spends a short period of time in the shell gland, then shell thickness will be less. Also, the time of day when the egg is laid will also determine the thickness of the shell. In general, the earlier in the day or light portion of the photoperiod the thicker the shell will be. The amount or rate of calcium deposition will also affect the thickness of the shell. Some strains of birds may be able to deposit calcium for the egg shell at a faster rate than others.
Another factor such as the age of the hen plays a role in determining the functional quality of the egg shell. As the hen ages, the thickness of the shell usually declines. Other egg shell quality factors such as the formation of abnormal ridges, calcium deposits, or body checks (ridges) are important considerations in determining egg shell quality. The asthetic quality of egg shells relate to the quality factors which the consumer can see, such as soundness of the shell, cleanliness of the shell, shape of the shell, and color of the shell. Several factors do affect asthetic egg shell quality.
Factors such as wash water temperature which affects the incidence of “thermal” cracks, moisture condensation on the shell, refrigeration temperature, and mechanical handling of the egg all affect the asthetic quality of the egg shell. Microbiological contamination of the inside of the egg is greatly affected by the ability of the egg shell to stop the invasion of micro-organisms and bacteria from entering the egg through the shell’s pores. When the cuticle or bloom is deposited by the hen on the shell this acts as a barrier to keep bacteria from entering the egg.
When eggs are washed, however, this removes most if not all of the cuticle from the shell surface. Thus, bacteria have an easier time entering the egg after washing. Even when the cuticle is removed, the two inner shell membranes help prevent bacteria from entering the egg. These barriers provide a good line of defense against invading bacteria. Many factors can contribute to the conservation of good egg shell quality. If the egg producer manages his flock in the proper manner by providing the roper nutrition and environmental conditions, then high egg shell quality should be achieved. A specific procedure that a producer should do to assure the production of eggs with good egg shell quality is to avoid scaring the birds so that the egg spends the normal amount of time in the shell gland. A key item to remember is to not stress the flock in any manner. Although it may not be practiced, the use of a “ahemeral” lighting program has shown to be effective in causing eggs to spend a longer time in the uterus, thus, producing eggs with thicker shells.
Nutritionally speaking, it is important for the producer to feed a ration properly formulated with the correct amount of calcium and phosphorus in the diet (usually 3. 5-3. 75% calcium, . 45% phosphorus). The production of eggs with thick, strong shells usually occurs from young vs. older flocks. Thus, a producer should expect more shell breakage and eggs produced with thinner shells to occur with older flocks and those producing eggs a couple of months after they’ve been molted. It is also important for the producer to monitor the health of the flock.
Since diseases such as Infectious Bronchitis and Newcastle cause egg shell abnormalities in the texture of the shell and shape of the shell, producers should continually monitor their flock for these diseases and follow management practices to avoid their flock from contacting these diseases. One of the egg shell quality problems that often occurs is the production of eggs having body checks. These are eggs which are cracked in the uterus during shell formation, then the egg shell forms on top of the crack.
Robert Bastian reported in a newsletter published by the University of Georgia (Commercial Egg Tips) ways for producers to reduce the problem of body checks. His recommendations were to: 1) avoid overcrowding of hens in cages which produces body checked eggs because hens contact themselves and the sides of the cage, 2) use flocks that are of a relatively young age because older flocks produce more body checked eggs, and 3) use a lighting program which is no longer than the longest natural light in open houses.
There are several procedures that need to be followed in order to conserve the asthetic quality of egg shells. The frequent gathering of eggs will help prevent the accumulation of dirt and stains on the shell. In addition, when eggs are washed the temperature of the wash water should be about 20°F warmer than the eggs. This will help prevent the occurrence of thermal cracks or “blind checks” as they are sometimes called.
Today’s in-line commercial gathering of eggs has helped reduce the incidence of checked and cracked eggs, but producers should still be aware of problems in the collection system that could damage eggs. As far as procedures followed to conserve micro-biological contamination of egg shells, appropriate washing and egg processing techniques should be followed. The use of the proper sanitizing agent is very important to maintaining egg shell cleanliness and free from bacterial contamination.