1. The Female Reproductive Tract
Virtual Chicken
The Science Behind the Egg
The Female Reproductive Tract

2. Virtual Chicken The Female Reproductive Tract
Graphic from American Egg Board website at

3. Virtual Chicken The Female Reproductive Tract
Egg Structure
Cuticle
Shell
Membranes
Albumen
Yolk

4. Virtual Chicken The Female Reproductive Tract
Cuticle
Acts as a lubricant during the laying process
Plugs pores
Reduces moisture and gas loss
Breaks down over time
Can be damaged during washing

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Shell
Color determined by breed or strain of bird
Composed almost entirely of calcium carbonate with small amounts of sodium, potassium and magnesium
Serves as a package for contents
Contains thousands of pores

6. Virtual Chicken The Female Reproductive Tract
Shell Membranes
Two protein fiber membranes
Separate to form air cell
Air cell increases as moisture and carbon dioxide is lost from the egg.

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Albumen
White/clear portion of egg contents
Four distinct layers
Water is primary component
Egg quality determination

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Yolk
Vitelline membrane surrounds yolk
Good source of nutrients
The composition of yolk lipid is about
65.5% triglyceride, 28.3% phospholipid,
and 5.2% cholesterol.
Fatty acid composition in the yolk is influenced by the type of fat in the hen’s diet

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Egg
Component %
Protein
Lipid
Carbohydrate
Ash
Albumen
0.03
Yolk
1.1
Whole Egg

10. Virtual Chicken The Female Reproductive Tract
How would you describe a high quality egg?

11. Virtual Chicken The Female Reproductive Tract
Quality measurements:
Air cell size
Albumen height and diameter
Vitelline membrane strength

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Air cell
Generally the larger the air cell the older the egg
Measured by candling

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How could you rapidly age an egg so that the air cell would increase in size?

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Refrigeration keeps the air cell small so you could rapidly age the egg by exposing it to higher temperatures.
1 day at room temperature equals 7 days in the refrigerator

15. Virtual Chicken The Female Reproductive Tract
Albumen height and diameter
A thicker more compact albumen denotes higher quality

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Which egg is higher quality? Why? A B

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The one labeled A is higher quality because the albumen (egg white is more compact) and the height of the yolk and albumen is higher indicating there has been less breakdown of the vitelline (yolk) membrane and albumen.

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Vitelline Membrane
As the vitelline membrane ages:
it becomes easier to break
it stretches and the yolk flattens
it allows more moisture to move between the yolk and albumen

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Egg Safety
Until the 1990’s, the contents of an intact eggs was thought to be sterile
1 in 20,000 raw eggs have a chance of being contaminated with Salmonella Enteritidis
Eggs should be thoroughly cooked before eating

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Can you get avian influenza from eating an egg?

21. Virtual Chicken The Female Reproductive Tract
No. The temperatures during pasteurization and cooking eggs and egg products is more than adequate to inactive any virus.
For more information visit

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Nutrition
Egg protein is of such high quality that it is used as the standard by which other proteins are compared.
Eggs have a biological value (efficacy with which protein is used for growth) of 93.7%.
Comparable values are 84.5% for milk, 76% for fish, and 74.3% for beef.
Egg yolk contains lecithin which is a good emulsifier.
Egg contain every essential amino acid, fatty acid, vitamin (except vitamin C) and mineral needed by humans.

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Cholesterol
Some individuals are more sensitive to the effects of dietary cholesterol (15-20% of the population)
All the cholesterol in an egg is found in the yolk not in the white

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For more information on nutritional benefits from eggs go to

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Trivia*
A hen requires 24 to 26 hours to produce an egg. Thirty minutes later, she starts all over again.   
The egg shell may have as many as 17,000 tiny pores over its surface. Through them, the egg can absorb flavors and odors. Storing them in their cartons helps keep them fresh.   
Eggs age more in one day at room temperature than in one week in the refrigerator.   
About 240 million laying hens produce approximately 5.5 billion dozen eggs per year in the United States.   
*American Egg Board website

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Trivia continued:
White shelled eggs are produced by hens with white feathers and ear lobes. Brown shelled eggs are produced by hens with red feathers and red ear lobes.  
To tell if an egg is raw or hard-cooked, spin it! If the egg spins easily, it is hard-cooked but if it wobbles, it is raw.   
If an egg is accidentally dropped on the floor, sprinkle it heavily with salt for easy clean up.
Egg yolks are one of the few foods that naturally contain Vitamin D. 
Yolk color depends on the diet of the hen. Natural yellow-orange substances such as marigold petals may be added to light-colored feeds to enhance colors. Artificial color additives are not permitted.   
Occasionally, a hen will produce double-yolked eggs throughout her egg-laying career. It is rare, but not unusual, for a young hen to produce an egg with no yolk at all.

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Summary:
Structure: You can learn a lot about the egg by analyzing its structure.
Quality: Quality can be measured by visually observing the broken out egg.
Safety: Storing eggs in the refrigerator and cooking them thoroughly before eating will insure egg safety.
Nutrition: Egg are an economical nutrient dense food.