There is the joke that white milk comes from white cows and chocolate milk comes from brown cows but what about chickens? White chickens do produce white eggs and brown chickens do produce brown eggs. Beyond the genetic components, what other factors are affecting the color of an egg? Is egg color a sign of hen health?
History of egg coloring
Across societies and religions, eggs represent life and renewal. Decorating eggs became a central part of Easter celebrations when the Christian community started dying eggs red to represent the blood of Christ and then giving them as gifts. The red has adapted to the many colorful and cultural eggs we see today. However, looking in the fridge or on the counter, there are naturally various colors of eggs. How can one chicken produce eggs that are different shades and what does the color indicate about the health of the hen laying it?
Genetics play the largest role
Eggshell color is genetically determined according to the breed of the layer. The brown color of some eggs comes from a pigment called protoporphyrin, which results from the breakdown of the red pigment hemoglobin; the same pigment that gives blood its red color. The availability of either white or brown eggs in the store is largely determined by culture. Overall, the percentage of eggs produced globally is equal between white and brown. It is known that the shells of brown eggs are stronger than white eggs and contain a thicker cuticle (more pigments in it).
Factors regarding color
Genetics: Eggshell color is largely determined by genetics but considerable variation in shell color can still be seen within a genetically similar flock.
Disease: Some diseases damage the oviduct and affect egg production. Infectious Bronchitis has the most influence on changing shell color.
Nutrition: Though it typically has little effect on shell color, nutrient deficiency can influence the process of egg and shell development. Certain drugs result in pale eggs (nicarbazin).
Age: Pale eggs are more common in older flocks. The reason for this is the egg is larger but the amount of pigment provided during shell formation is the same.
Sunlight: In free-range flocks, pale eggs are more likely to occur than in closed houses. The reason for this could be an overdose of vitamin D3 available to the birds.
Parasites: Infestation of roundworms or capillaria worms may cause pale shells and pale yolk. By damaging the intestinal wall, there is reduced nutrient absorption for egg and eggshell development.
Stress: Three to four hours before the egg is laid, the bulk of the pigment is transferred to the shell. Therefore, an early egg may not have enough pigment deposited. However, if the egg is kept longer in the oviduct, due to stress, it may cause a thin layer of calcium to be deposited; giving the egg a grayish-white appearance.
Production rate: In some cases, there is a link between the production rate and the eggshell color. Therefore, eggshell color can be lighter in high-producing flocks.
For centuries, eggs (of all colors) have served as a nutritious source of food and a symbol of renewal. Every breed of layers has a standard ideal shell color. By being aware of this expected color, producers can evaluate if the hen house is facing any issues. Generally speaking, a dark pigment indicates a healthy hen but factors—like age and sunlight—can alter the eggshell without a detrimental cause.