Factors which may affect shell color

This erudite artircle is reproduced in part from The University of Florida IFSAExtension for the full text click here http://edis.ifas.ufl.edu/vm04 Authors Factors Causing Poor Pigmentation of Brown-Shelled Eggs 1 Gary D. Butcher and Richard D. Miles2

Once the egg reaches the site of the reproductive tract known as the uterus (shell gland), it resides there for approximately 20 hours. During this time the shell is deposited, mostly as calcium carbonate, onto the shell membranes that envelop the albumen and yolk. As shell formation progresses in the brown egg layer, the epithelial cells lining the surface of the shell gland begin to synthesize and accumulate the pigments. The three main pigments are biliverdin-IX, its zinc chelate, and protoporphyrin-IX. The most abundant pigment in today's commercial brown-shelled eggs is protoporphyrin-IX. It is not until the final 3 to 4 hours of shell formation that the bulk of the accumulated pigment is transferred to the protein-rich, viscus fluid secretion known as the cuticle. The degree of brownness of the hen's eggshell is dependent on the quantity of pigment directly associated with the cuticle. The pigment-rich cuticle is deposited onto the eggshell at about the same time shell deposition reaches a plateau, about 90 minutes prior to oviposition. Therefore, pigment distribution is not uniform throughout the thickness of the eggshell. Even though the eggshell contains traces of pigment, its contribution to the intensity of brown color is negligible compared to that of the cuticle.

Stress . Since the majority of the pigment is localized in the cuticle, anything that interferes with the ability of the epithelial cells in the shell gland to synthesize the cuticle will affect the intensity of eggshell pigmentation. This is especially true during the final 3 to 4 hours of shell deposition since it is during this time in the egg-laying cycle that cuticle synthesis and accumulation occur most rapidly.

Stressors in poultry flocks such as high densities, handling, loud noises, etc., will result in the release of stress hormones, especially epinephrine. This hormone, when released into the blood, is responsible for causing a delay in oviposition and the cessation of shell gland cuticle formation. The above stressors, which result in hen nervousness and fear, can cause pale eggshells to be produced. The paleness is often the result of amorphous calcium carbonate deposited on top of a preexisting fully formed cuticle or of an incomplete cuticle caused by premature arrest of cuticle formation.

Brown-shelled birds, especially broiler breeders, housed in experimental floor pens for research purposes often become fearful each time the pen is entered for such things as egg collection, vaccination, uniformity, and frame and fleshing measurements. When this occurs, production of pale-shelled eggs should be expected, especially if the fearfulness occurs during the last 3 to 4 hours of the egg-laying cycle when the cuticle formation is interrupted. In fact, the relationship between stress and the production of pale eggs by laying hens is so great that researchers have suggested that loss of shell pigment may provide a basis for a noninvasive method of assessing stress in hens.

Age of the bird . As the brown egg-type bird ages, there is a corresponding decrease in eggshell pigment intensity. The exact reason for this is unknown. It is possibly due to the same quantity of pigment being dispersed over a larger surface area of shell as egg size increases with bird age or less pigment synthesis. As the hen ages it is normal for the tapered end of the egg to contain less pigment than the rounded end. Stress-related egg retention in the shell gland and subsequent amorphous calcium carbonate deposition on the shell surface have been identified as a major cause of pale eggs in older hens.

Chemotherapeutic agents . A rapid decline in shell pigmentation is common following the ingestion of certain drugs by the hen, such as the sulfonamides. The coccidiostat Nicarbazin, administered to hens at a dose of 5 mg per day, can result in the production of pale eggs within 24 hours. Higher doses can lead to complete depigmentation of the eggshell cuticle.

Disease . Viral diseases, such as Newcastle and infectious bronchitis, affect egg production in poultry. These viruses have a specific affinity for the mucus membranes of the respiratory and reproductive tracts. Because the virus directly infects and damages the reproductive tract, the signs of disease are manifested indirectly in the product of the tract, the egg. Thus, total egg numbers decline and eggshells become thinner and abnormally pale and have irregular contour. Internal quality is also adversely affected (watery whites). These egg production and quality problems can persist for extended periods of time.

Most eggshell pigments are located in the cuticle and outer portion of the calcified eggshell. Premature arrest of cuticle formation or release of stress-related hormones (epinephrine) will result in the production of pale brown-shelled eggs. Age of the bird, use of certain chemotherapeutic agents, and disease also can affect the intensity of pigmentation.

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Solomon, S. E. 1992. A question of color. Shaver Focus 21(2):2-3.

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This document is VM94, one of a series of the Veterinary Medicine-Large Animal Clinical Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May, 1995. Reviewed March, 2009. Visit the EDIS Web site at http://edis.ifas.ufl.edu.

Gary D. Butcher, Poultry Veterinarian, and Richard D. Miles, Poultry Nutritionist, Department of Dairy and Poultry Sciences, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.

Links for further reading and research

Suggested effects of sunlight and stress on egg shell colour

Link to Tim Adkerson's paper - A Review of Egg Color in Chickens

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