Group Title: Poultry Science mimeograph series
Title: Egg shell texture and egg quality
Full Citation
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 Material Information
Title: Egg shell texture and egg quality
Alternate Title: Poultry Science mimeograph series - University of Florida ; PY64-2
Physical Description: 6 p. : ; 28 cm.
Language: English
Creator: Tarver, Fred R. Jr. ( Fred Russell )
Donor: unknown ( endowment )
Publisher: Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: July, 1963
Copyright Date: 1963
Subject: Eggs -- Quality -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: by Fred R. Tarver, Jr.
General Note: Caption title.
General Note: "July 1963."
 Record Information
Bibliographic ID: UF00094223
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 318812329

Full Text

S-a. Poultry Science Florida Agricultural
Mimeograph Series No. PY64-2 Experiment Station
200 Copies Gainesville, Florida
July, 1963


by Dr. Fred R. Tarver, Jr.
Assistance Poultry Husbandman

Overwraps for packages, particularly as they pertain to food items,

should contain the product, should protect the product and should aid in

merchandising the product. This includes manufactured as well as bio-

logical type overwraps of which the egg shell comes within the scope of

the latter. The shell of the birds egg is relatively smooth, hard,

calareous coat, attached to the outer of the two shell membranes. So firm

is the attachment that the shell and membrane can be separated only with

difficulty. Eggs show great variety in the surface characteristics of

their shells. Some are exceedingly glossy, others very dull; some are

smooth, some rough. Textures intermediate between the extremes are common.

The shell is deposited around the egg materials in a section of the

reproductive tract referred to as the shell gland or uterus. The wall

of the shell gland does not act as a resevior for calcium carbonate prior

to the eggs entrance into this area. But once the egg is positioned in

the shell gland, the wall secretes calcium carbonate supplied by the blood.

Stores of calcium carbonate must be available in areas of the hens body

which can be drawn upon rather quickly during the time in which the shell

is being deposited. This has been verified by the fact that the calcium

level in the blood of a layer when an egg is not in the oviduct and a non-

layer is essentially the same. When the comparison is made between the


two after the egg is in the uterus, the layer's blood calcium level has

markedly increased over that of the non-layer. The whole mechanism of

shell deposition is believed to be triggered by an enzyme(s) referred to

as carbonic anhydrase. If this is inhibited malformation will occur.

What is the structure of the egg shell? Starting with the outer sur-

face we have mucin, which is deposited on the shell as the egg passes

through the vagina of the hens reproductive tract. This material serves

the purpose of not only placing a bloom on the shell but also stopping

or plugging the pore openings in the shell. Next we have the mammillary

layer that is referred to as the spongy layer. So named because once all

the calcium carbonate has been removed, a spongy like structure remains

which is composed chiefly of protein. Next we have the mammillary core

of the inter most terminal of the spongy layer which comes in contact

with the outer shell membrane. In the cross section of the shell from

the outer surface to the inter most surface, we have what is referred to

as pores of which 7500 may be found in any one egg shell. The process of

depositing the shell takes approximately 12 hours.

Several factors may effect the shell texture. Among these, we should

consider species variation, the influence of heredity, effective nutrition,

drugs, physiological, anatomical factors and diseases. The egg of certain

ducks are noticeable oily to the touch and those of the ostrich are pitted

with large pores. The shell of the domestic hens egg may be mat or fairly

lustrious. Its many variations in surface texture make it difficult to

designate abnormalities. Ridged and furrows are frequently present. Small

sandy deposits of calcareous material are often found at one end or the

other or occasionly distributed over the entire shell. On brown eggs many

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superficial deposits are sometimes noticeable as white spots. According

to the U.S.D.A. standards for shell, shape and texture, a normal egg is

oval in shape and one end larger than the other and it tapers toward the

smaller end. Eggs that are unusual in shape such as those having ridges,

rough areas, or thin spots are placed in lower grades such as B and C

quality. Shells of such eggs are usually weaker than normal shells and a

danger of breakage in route to the consumers lowers the utility value of the

egg. Eggs of abnormal shape also lack consumer appeal. Therefore they are

excluded from the better grades. Glossy and chalky shells appear to be

controlled at least to some extent by heredity. Daughters tend to re-

semble the dam with respect to the smoothness or roughness of shell eggs.

The influence of nutrition on shell texture is still a subject of

investigation. Experiments have not demonstrated conclusively what

deficiency in the diet, if any, can be held accountable for the numerous

abnormalities that occur on the shell surface. Excessive amounts of

calcium in the diet can have adverse effects upon production and egg size

and may have some influence upon thickness of the shell. As yet nutrition

has not been incriminated as a factor contributing to rough shell surface.

In recent years, drugs, insecticides and fungicides have been incriminated

as being directly responsible for the formation of abnormal shell texture

in one form or another. The sulfonamides produce marked irregularities in

the surface of the egg shell and are characterized by granular deposits on

the shell surface. Feeding Nicarbazine to laying hens has been found to

produce eggs with blemished yolks which in its most serious form have the

appearance of rotten eggs. The rate of egg production can be markedly re-

duced. Egg size can be reduced. The shell of brown eggs can be rendered

white by incorporating Nicarbazine in the diet of heavy breed hens. Nicar-


basin as you well know is added to the diets of young chickens as a cocci-

diostat. Arasan has been used as a fungicidial material in grains which may

eventually find their way into the diets of birds. This material is used

in the amounts of 800 to 1000 p.p.m. for the purpose of protecting the grain

against fungus and if Arasan is removed in an acceptable manner prior to its

use in feeds, it does not have any dilitarious effect on the eggs. Certain

states require that Arasan treated grains be dyed so they may be separated

from those not treated with Arasan. Arasan effects egg quality by a reduction

in shell thickness, weakened albumen, misshapen and prematurely laid eggs with

little or no shell disposition. This condition actually has been confused

in many instances with certain type infectious diseases that have dilitarious

effect on shell quality.

Physiologically, shell texture is produced by glandular secretion.

The egg is glossy for example when an abundant deposit of organic material,

cuticle or mucin, is on the surface of the shell. Glandular activity depends

in part upon certain aspects of anatomical structure such as the size and

number of secretary cells within the shell gland. For this reason, the in-

dividual egg tends to resemble one another in shell texture. Cycle of laying

has its effect upon smoothness or roughness of the shell. Normally the first

egg in any egg cycle is the smoothest with the shell becoming progressively

rougher as the cycle continues. As to anatomical obstructions, the isthmus

may cause the egg shell to contain ridges if the shell membranes were wrinkled

at the time the shell is deposited.

Diseases occurring in laying flocks may cause certain abnormalities in

shell texture. Inferior egg quality has frequently been observed follow-

ing outbreaks of respiratory diseases. These would include Newcastle disease

and infectious bronchitis. Damage caused by these two diseases includes a

- 5 -

striking reduction in egg size, poor shell quality meaning (thins, sandy or

heavily ridged egg shell or grossly misshapened eggs) and decrease in albumen

quality. Not to mention the possibility of egg production dipping to zero

during the time in which the infection is running its course. Laryngo6

tracheitis effects shell quality as well as interior quality. These shell

deformities resemble those caused by Newcastle and infectious bronchitis.

Many of the egg shell irregularities have been observed, but it might

be well to mention some of their characteristics. The shell may appear

wrinkled or ridged sometimes over its entire surface, sometimes over only a

portion of its surface. Occasionally a single ridge extends around the

equatorial region of the egg, so that the two halves of the shell appear to


In some instances, a portion of the shell may be missing and the shell

membrane partically exposed. The surface of the shell sometimes displays ir-

regularities consisting of small deposits of calcareous material in a form

of folds, tiny protuberances or small extentions at either end of the egg.

Occasionally, nodules of calcareous materials are scattered over a shell

membrane which is otherwise bare. The shell of the hens egg is translucent

when the egg is laid, but becomes opague as soon as it dries. By transmitted

light, most eggs appear uniformly translucent. Occasionally, an egg shows

numerous bright flecks in its shell. These are due to the present of

aggrigations of protein which retain moisture better than other parts of the

shell and pass light more readily. These may be viewed by a chandler and mis-

taken for cracks or checks in the shell.

In addition to many of the factors in which we have mentioned, environ-

ment, management, per se, may also contribute to abnormalities existing on


the surface of the shell. We certainly know that temperature has a marked

effect on calcium utilization which inturn causes thin shells. This ad-

versely affects the overall quality of eggs.

You can readily observe that many factors either independently or

collectively can influence shell texture and egg quality.

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