Fenceline Chatter: Why are eggs different colors?

Lonnie Jenschke
Special to the Empire-Tribune

Have you ever been curious about why chicken eggs can be different colors? While most eggs are white or brown, they also come in colors like cream, pink, blue and green. In addition — and this is no “yolk” — some are even speckled.

Lonnie Jenschke

Nature has provided chickens with diverse color patterns for their feathers, skin patches and eggshells for various 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 mainly determined by the chicken’s genetics. That means the breed of hen will usually indicate what color of egg will be produced.

Chicken earlobes help predict egg color

You’ve got to hear this … a good way to guess what color eggs a chicken will lay is to take a gander at the hen’s ear lobes.  

Generally, hens with white earlobes will produce white eggs. But all eggs start out white because the shells are made from calcium carbonate. They get their color from the hen’s genetics as the egg forms.

Chicken egg formation

Different eggshell colors come from pigments deposited onto the shell as the egg forms in the hen’s oviduct. The oviduct is a tube-like organ found along the hen’s backbone between the ovary and the tail.

A chicken yolk, or ovum, forms in the hen’s ovaries. A fully formed ovum leaves the ovary and makes its way into the oviduct. There, it goes through a five-stage process to help ensure the yolk makes it safely to the outside world. The entire egg-forming process usually takes a little more than 24 hours.

It’s during the fourth stage of this process involving the shell gland that pigments are deposited onto the shell, producing its color. So, in short, different breeds of chicken deposit different pigments on the shell as it forms, changing its exterior — and sometimes its interior — shell color.  

A pigment of your imagination 

A pigment called oocyanin is deposited on the egg of the Ameraucana breed, penetrating both the exterior and interior of the shell and making 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 rooster from a brown-egg-laying and a blue-egg-laying breed. The hen produces a brown pigment that penetrates the blue shell of the egg, resulting in a greenish-hued egg. The darker the brown pigment, the more olive-colored the egg appears.  

Egg-straneous factors change shell color, shape

While genetics primarily determine egg color, other factors can also influence the color and other characteristics of the shell. These factors include a hen’s age, diet, environment and stress level.

While not directly associated with color, an oddly or irregularly shaped egg may occasionally pop out. This may result from a problem during the hen’s egg-forming process.

Very old and very young hens are the most likely to lay abnormally shaped eggs.

All things yolk: Color, nutrients, and double yolks

You may also be wondering if the color of the egg affects the color of the yolk. Well, it doesn’t, but the hen’s diet certainly does. For example, if a pasture-raised hen eats plants with yellowish-orange pigmentation, the yolks can take on a more orange color. If she eats mainly a corn- or grain-based diet, the yolk is more likely to be a pale yellow.

A double yolk is a fluke that occurs when a hen ovulates too rapidly, releasing two yolks, usually about an hour apart. These yolks go into the oviduct and eventually wind up in the same shell.

Where can you learn more about chickens and eggs? Well, you could go to the “hen-cyclopedia” of course. But if you don’t have one handy, visit the AgriLife Extension website https://tx.ag/ChickensEggs for more information.

Lonnie Jenschke is the Erath County Extension Agent – Ag/NR for the Texas AgriLife Extension Service. He may be contacted at lonnie.jenschke@ag.tamu.edu