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United States Department of Agriculture

Agricultural Research Service

Title: Shell Egg Quality

Author
item Jones, Deana

Submitted to: National Egg Quality School Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 6, 2004
Publication Date: October 11, 2004
Citation: Jones, D.R. 2004. Shell egg quality. National Egg Products School Proceedings. Meeting Abstract. p. 11-15.

Interpretive Summary: The goal of all producers is to produce a better product. In the shell egg industry, this translates to producing a higher quality egg. Egg quality can be defined in many ways. The American consumer demands a clean and sound egg that looks appealing when cracked into a skillet. The shell egg producer could define egg quality in terms of being relatively free of defects which would result in a downgrade. There are many factors, both interior and exterior, that determine the grade of a shell egg at the point of retail. In the US, eggs can be marketed as grades AA, A, or B. Most shell eggs in the US market are sold as 'Grade A'. The USDA Agricultural Marketing Service (USDA-AMS) is responsible for determining what factors contribute to the down-grading of a shell egg. Currently, all regulations governing shell egg grades are based on physical quality attributes. A complete description of these factors can be found in the USDA Egg Grading Manual (USDA, 2000). Egg grades are determined by either hand candling or breaking out the egg. During hand candling, a light is shown through the egg shell to allow the grader to examine the clarity and quality of the albumen and yolk. The size of the air cell can also be estimated. All these factors, along with other exterior factors are combined for a grade assignment. Defects which would render the egg inedible can also be detected during hand candling. A more precise measurement of egg interior quality is the Haugh unit (Haugh, 1937). During this examination, the egg is broken out onto a flat surface, usually a break-out table, and the height of the thick albumen is measured with a micrometer. The Haugh unit is a correlation between egg weight and albumen height. While the Haugh unit is a more precise measurement of egg quality, it destroys the egg during analysis, so hand candling is the more common form of egg quality determination for grade. The USDA-AMS has also established guidelines for consumer weight classes of shell eggs. These weight classes exist to ensure the consumer is receiving a full dozen of appropriately sized eggs and not a mixed grab-bag. Table 1 is a summary of the required weight classes for commercial shell eggs. The six allowable egg sizes and the corresponding minimum weights of individual eggs within a dozen, dozens, and 30 dozen cases are presented. There are many factors that can affect egg quality. These can include nutrition, breed, management, egg temperature, and processing methods. Therefore, when attempting to enhance egg quality, a producer must consider both production and processing factors. Table 1. Weight class requirements for shell eggs. Size Minimum net weight for individual eggs in a dozen (ounces) Minimum net weight per dozen (ounces) Minimum net weight for a 30 dozen case (pounds) Jumbo 29 30 56 Extra large 26 27 50.5 Large 23 24 45 Medium 20 21 39.5 Small 17 18 34 Peewee -- 15 28 Hen nutrition can have a direct effect on egg quality. When a hen is nutritionally compromised, the body begins to shut down unnecessary processes. Reproduction is greatly diminished, and the bird becomes immunologically compromised which can lead to increased incidence of disease. If a layer diet is complete except for a lack in the appropriate level of the amino acid lysine, a laying hen will not efficiently produce eggs and the eggs laid will be of inferior quality. A lack of calcium and phosphorus in the layer diet will result in the hen leaching these minerals from the bones in order to lay sound eggs. As this condition progresses, the hen will reach a point where it will no longer removed minerals from the bones. After this, a hen will produce soft shell or even shell-less eggs. A layer diet should be formulated by a trained nutritionist to ensure all nutrient requirements are met. Minimizing physiological stress within the hen

Technical Abstract: The goal of all producers is to produce a better product. In the shell egg industry, this translates to producing a higher quality egg. Egg quality can be defined in many ways. The American consumer demands a clean and sound egg that looks appealing when cracked into a skillet. The shell egg producer could define egg quality in terms of being relatively free of defects which would result in a downgrade. There are many factors, both interior and exterior, that determine the grade of a shell egg at the point of retail. In the US, eggs can be marketed as grades AA, A, or B. Most shell eggs in the US market are sold as 'Grade A'. The USDA Agricultural Marketing Service (USDA-AMS) is responsible for determining what factors contribute to the down-grading of a shell egg. Currently, all regulations governing shell egg grades are based on physical quality attributes. A complete description of these factors can be found in the USDA Egg Grading Manual (USDA, 2000). Egg grades are determined by either hand candling or breaking out the egg. During hand candling, a light is shown through the egg shell to allow the grader to examine the clarity and quality of the albumen and yolk. The size of the air cell can also be estimated. All these factors, along with other exterior factors are combined for a grade assignment. Defects which would render the egg inedible can also be detected during hand candling. A more precise measurement of egg interior quality is the Haugh unit (Haugh, 1937). During this examination, the egg is broken out onto a flat surface, usually a break-out table, and the height of the thick albumen is measured with a micrometer. The Haugh unit is a correlation between egg weight and albumen height. While the Haugh unit is a more precise measurement of egg quality, it destroys the egg during analysis, so hand candling is the more common form of egg quality determination for grade. The USDA-AMS has also established guidelines for consumer weight classes of shell eggs. These weight classes exist to ensure the consumer is receiving a full dozen of appropriately sized eggs and not a mixed grab-bag. Table 1 is a summary of the required weight classes for commercial shell eggs. The six allowable egg sizes and the corresponding minimum weights of individual eggs within a dozen, dozens, and 30 dozen cases are presented. There are many factors that can affect egg quality. These can include nutrition, breed, management, egg temperature, and processing methods. Therefore, when attempting to enhance egg quality, a producer must consider both production and processing factors. Table 1. Weight class requirements for shell eggs. Size Minimum net weight for individual eggs in a dozen (ounces) Minimum net weight per dozen (ounces) Minimum net weight for a 30 dozen case (pounds) Jumbo 29 30 56 Extra large 26 27 50.5 Large 23 24 45 Medium 20 21 39.5 Small 17 18 34 Peewee -- 15 28 Hen nutrition can have a direct effect on egg quality. When a hen is nutritionally compromised, the body begins to shut down unnecessary processes. Reproduction is greatly diminished, and the bird becomes immunologically compromised which can lead to increased incidence of disease. If a layer diet is complete except for a lack in the appropriate level of the amino acid lysine, a laying hen will not efficiently produce eggs and the eggs laid will be of inferior quality. A lack of calcium and phosphorus in the layer diet will result in the hen leaching these minerals from the bones in order to lay sound eggs. As this condition progresses, the hen will reach a point where it will no longer removed minerals from the bones. After this, a hen will produce soft shell or even shell-less eggs. A layer diet should be formulated by a trained nutritionist to ensure all nutrient requirements are met. Minimizing physiological stress within the hen can also enhance shell egg quality. During periods of stress there is a breakdown of the reproductive tract. This can lead to reduced egg quality or production. This breakdown can also lead to an increase in the incidence of meat spots. Acute changes in the bird=s environment can result in a stress response. Exposure to disease can result in a decrease in shell egg quality. Many diseases can impair the reproductive tract. An example is infectious bronchitis. Initially this disease causes a respiratory response. It is then able to move through the blood stream and infect the reproductive tract. This can cause decreases in the internal and external quality of eggs produced. Both young chicks and adult hens can be infected producing these results. Infectious bronchitis is caused by a coronavirus and is very contagious disease among chickens. Within 1-2 days, almost 100 % of a flock can show signs of the disease (Trampel, 2004). During the course of infectious bronchitis, oviduct weight and length is reduced and remains so for approximately 3 weeks. There is also a decrease in the number and height of epithelial cells in the lining of the oviduct. Another complication that can occur is the development of false layers. Soft shelled eggs or fully formed eggs are found in the abdominal cavity of a false layer. This comes about due to the egg progressing through the reproductive tract and reverse peristalsis occurring at some point forcing the egg to be deposited in the abdominal cavity. The age of the laying flock can also have a direct effect on egg quality. The longer a hen is in lay, the lower the quality of the eggs produced. As the hen ages, the reproductive tract begins to decline. This results in a decrease in egg quality. Molting a laying flock can serve as a means of rejuvenating the reproductive tract. There are concerns associated with the act of molting and it should be performed in a responsible manner. After a molt, egg quality is enhanced, but declines at a greater rate than during the previous production cycle. Molting a flock multiple times also results in a greater rate of egg quality decline. Management practices can have a profound effect on egg quality and are some of the easiest to fix. Maintaining the hens on a set lighting schedule can enhance egg quality and egg production. Providing a clean environment aids in maintaining bird health. Proper handling of the birds reduces in the incidence of body checks. A body check occurs when the egg is cracked in the reproductive tract and the bird is then able to mend the crack. These eggs are considered to be Aless sound@ than a normal shell egg. A trauma that would result in the cracking of the egg within the hen would be required. For this reason, proper employee training is imperative. Proper maintenance of production equipment can also improve egg quality. Collection belts which are working improperly can result in an increase in the incidence of impact checks. An impact check is a cracked egg, which has intact membranes, that resulted from two eggs colliding. Repairing cages to prevent protruding wires decreases the risk of cracked eggs. Proper cleaning of belts, cages, and collection flats reduces the risk of shell contamination with egg contents, feed and fecal matter. In the US, adhering matter results in a grade of Ainedible@. These eggs can not be sold for human consumption. Egg processing has a definitive effect on shell egg quality. There are many steps in the processing procedure where egg quality can be enhanced. When the egg is laid it is approximately 103 F (39.4 C). The quicker an egg is cooled, a greater level of interior quality is maintained. The longer the internal egg temperature is above 45 F (7.2 C), the quicker the protein structures of the thick albumen and vitelline membrane breakdown. For this reason, care should be taken to ensure the egg is properly cooled throughout the shell egg processing procedure. One of these steps is the on-farm holding room. Collecting eggs from the laying house s

Last Modified: 7/31/2014
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