Davis: Why do chicken eggs have different colors? | Way of life


Have you ever been curious to know why chicken eggs can be different colors? Although most eggs are white or brown, they also come in colors like cream, pink, blue, and green. What’s more — and it’s not “yellow” — some are even speckled.

Nature has provided chickens with various color patterns for their feathers, skin patches, and eggshells for a variety of purposes including camouflage, protection from predators, and to signal individual identity.

According to a Texas A&M AgriLife Extension Service poultry specialist, the color of an egg is primarily determined by the genetics of the chicken. This means that the breed of hen will usually indicate the color of the egg that will be produced.

For example, Leghorn hens lay white eggs, while Orpingtons lay brown eggs, and Ameraucanas lay blue eggs. And the “olive egger” breed lays…wait…olive eggs.

But appearances aside, not all chicken eggs have major differences in taste or nutritional composition.

“In general, hens with white earlobes will produce white eggs,” said Gregory Archer, Ph.D., AgriLife Extension Specialist in the Department of Poultry Science, Bryan-College Station. “But all eggs start out white because the shells are made of calcium carbonate. They get their color from the genetics of the hen when the egg is forming.

Archer said chickens with lighter earlobes often also had white feathers and produced white eggs. Those with colored feathers and darker earlobes will likely produce colored eggs.

Nature has its own way of coloring eggs, and it doesn’t need boiling water, food coloring or paintbrushes. Different eggshell colors come from pigments deposited on the shell when the egg is formed in the hen’s oviduct. The oviduct is a tube-shaped organ located along the spine of the hen between the ovary and the tail.

A chicken yolk, or egg, forms in the hen’s ovaries. A fully formed egg leaves the ovary and enters the oviduct. There, he goes through a five-step process to ensure the yolk makes it safely to the outside world. The whole process of egg formation usually takes just over 24 hours.

It is during the fourth stage of this process involving the shell gland that pigments are deposited on the shell, producing its color. So, in short, different breeds of chicken deposit different pigments on the shell as it forms, changing the color of its outer – and sometimes inner – shell.

White Leghorn chickens lay eggs with white shells and breeds like Plymouth Rocks and Rhode Island Reds lay eggs with brown shells. The shells are brown because a pigment known as protoporphyrin is deposited on the shell. But since this happens late in the shell formation process, the pigment does not penetrate inside the shell.

Different breeds of chickens lay eggs of different colors or shades. The darker the feathers, the more likely the hen is to lay a brown or darker colored egg.

“That’s why when you open a brown egg, you’ll see that the inside of most of the shells remains white,” Archer said.

A pigment called oocyanin is deposited on the egg of the Ameraucana race, penetrating both the outside and the inside of the shell and turning them blue. Other breeds such as Araucana, Dongxiang and Lushi lay blue or blue-green eggs.

An olive egger results from a cross between a hen and a rooster of a brown-laying breed and a blue-laying breed. The hen produces a brown pigment which penetrates the blue shell of the egg, resulting in a greenish colored egg. The darker the brown pigment, the more olive-colored the egg appears.

Other chickens that lay colored eggs include the Easter Egg, Barred Rock, Welsummer, and Maran, with egg color depending on the breed and its genetics.

It turns out that the spots on the speckled eggs are just extra calcium deposits. One of the reasons for the speckled egg show is that speckles form when the calcification process of egg formation is disrupted. Another possible reason is a defect in the shell gland. Again, this could be the result of excess calcium in the hen’s system.

Oh, and while technically considered “abnormal”, speckled shells have sometimes proven to be tougher than regular shells.


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