Eggs come in a variety of colors, but the most common are white and brown. However, some breeds of chickens do lay blue or green eggs. So what causes eggs to be blue or green instead of white or brown? The main factor is genetics.
Genetics of Blue Eggs
The color of an egg is determined by the breed of chicken it comes from. Certain breeds have been selectively bred to produce blue eggs. The main breed that lays blue eggs is the Araucana chicken. The Araucana originates from Chile and gets its name from the Araucanía region. This breed possesses a genetic mutation that causes a protein called ovomacroglobulin to be overexpressed in the oviduct. Ovomacroglobulin contains biliverdin, a pigment that gives a blue-green color. When this protein is deposited on the eggshell as it forms, it leads to the blue-green egg color.
Some other breeds that can lay blue eggs include:
- Ameraucana
- Easter Egger
- Cream Legbar
These breeds likely have some Araucana genetics that enable them to also produce the bluish egg color. But the Araucana and Ameraucana are considered to be the primary pure breeds that lay blue eggs.
Biliverdin – The Source of Blue
As mentioned, the blue-green pigment in blue eggs comes from biliverdin. This is a pigment that comes from the breakdown of heme. Heme is a component of hemoglobin, the protein that carries oxygen in red blood cells. As red blood cells die and get recycled, the iron is removed from heme and it gets converted into biliverdin. This biliverdin is then normally further broken down into a yellow pigment called bilirubin.
In chickens with blue eggs, the biliverdin is not broken down as much. More of it remains to be deposited into the developing egg shell in the oviduct, leading to the blue-green color. The gene mutation in Araucana chickens somehow allows biliverdin to build up more than usual.
Amount of Biliverdin Affects Color
The exact shade of blue or green in an egg depends on the amount of biliverdin deposited into the shell. More biliverdin leads to a deeper blue-green color. Less biliverdin results in a lighter blue-green color. The biliverdin amount can be influenced by factors like the individual chicken’s genetics, diet, and health.
For example, a sick chicken may produce less biliverdin, leading to lighter colored blue eggs. And diet can affect biliverdin production too. Things like oxidative stress or ingestion of certain plant pigments may alter how much biliverdin builds up in the oviduct.
No Difference in Nutritional Value
Despite the different outer color, blue chicken eggs have no significant nutritional difference from brown or white eggs. The color is just a result of pigment deposition on the shell. It does not affect the quality of the egg inside.
Testing has shown that blue/green eggs have the same amount of calories, protein, vitamins, and minerals as any other colored eggs.
Rarity Increases Cost
Since blue eggs come from special breeds that are less common, they tend to cost more than white or brown eggs in the store. The rarity means fewer blue eggs are produced, but the higher demand keeps prices elevated.
On average, a dozen blue eggs can cost about $3-5 in the grocery store. That’s about twice as much as ordinary white eggs.
No Difference in Taste
Despite the outward color variation, blue chicken eggs taste the same as white or brown eggs. The different pigments in the shell do not penetrate deep enough into the egg contents to influence flavor.
When used in cooking and baking, blue eggs are indistinguishable from ordinary eggs in terms of taste. They can be substituted freely without impacting the end result.
Conclusion
In summary, blue eggs come from special breeds of chickens that have genetic mutations leading to overexpression of the pigment biliverdin. This blue-green pigment gets deposited onto the eggshell as it forms in the hen’s oviduct. While interesting to look at, blue eggs are nutritionally the same as other colored eggs. But due to the rarity of blue egg-laying breeds, they usually cost more at the store.