How Genetics Determine Duck Egg Color

Story by Marissa Ames. Leghorns lay white eggs and Marans lay dark brown eggs. But duck egg color doesn’t follow these specific rules. Why can some ducks, of the same breed, lay blue eggs while the others lay white? It’s not about what ducks eat. It has to do with genetics and how long the breed has been standardized. So, how do genetics determine duck egg color.

What Makes Eggs Different Colors?

There are two pigments responsible for egg colors, and they’re produced different ways.

Biliverdin, a green pigment, and blue oocyanin, are byproducts of bile and hemoglobin breakdown. If biliverdin and oocyanin present in eggshells, they permeate the entire shell, which is why blue and green eggs are colored on the inside as well as the exterior.

Brown and reddish color, which creates speckles and patterns, comes from protoporphyrines synthesized in the shell gland then secreted and deposited during the final stage of egg production. This explains why pigment on Marans chicken eggs can be rubbed off before the egg fully dries after laying and why the sooty Cayuga duck egg cuticle can be scrubbed off.

While white eggshells contain only protoporphyrin, blue and green shells contain both, in different amounts. This leads to blue, green, or olive-colored shells. Brown on the outside, green throughout.

Chicken egg colors follow breed standards: white-laying Leghorns, Welsummers with speckled shells, Marans with chocolate hues. Colors don’t deviate unless breeds cross. Blue didn’t present within modern chicken eggs until Araucanas arrived from Chile after 1914. Until then, eggs were shades of white to dark brown. Araucanas, then Ameraucanas and Legbars, standardized that blue egg. Hybrids carrying the dominant gene are Easter Eggers.

Green was the original duck egg color.

What Happened with Modern Ducks?

Once upon a time, all ducks were wild. Birds evolved to lay eggs which camouflaged with their surroundings. Birds laying within dark caves or holes would produce white shells while those laid in the open had pigment. Greener eggs matched riparian areas. Blue robin eggs hid within treetop canopies and speckled killdeer eggs blended against barren rock.

Wild mallards, the ancestor of almost all domestic ducks except Muscovies, lay light green eggs. But what happened to change duck egg color in domestic birds?

Blame breeders and aesthetics.

Though it’s believed they were first domesticated in Southeast Asia, ducks didn’t become popular in Europe for a while longer. Duck breeding became vogue in the 17^th century, about the same time Europeans started breeding chickens for more than just eggs. And Europeans liked the recessive white duck egg color. “Breed standards” developed in the Victorian Era and the original British Poultry Standard was published in 1865.

Duck egg color corresponds with the breeds’ histories within Europe.

Aylesbury ducks, which primarily lay white eggs, were recorded as “White English” in 1810 and dominated the first poultry show in 1845. These crossed with Chinese Pekins in 1873. Pekins were standardized a year later, and the white-feathered, white-laying ducks dominate the market today.

Indian Runner ducks also came from China but they came much later. Though they first appeared in the UK in 1835, they were first standardized after 1900. White eggs were still considered “pure” at that time. Around WWI, Joseph Walton attempted to “purify the breed” and obtain white-laying Runners. His attempts were so-so, and certain colors of Runners are more likely to lay white eggs.

John Metzer, of Metzer Farms hatchery, provides several possible reasons why eggs have developed to white versus green. One is that they were bred specifically for the white egg. “It’s also a guess,” says John, “that certain characteristics go hand in hand with blue eggs. In other words, maybe a large body size is on the same gene as white eggs. So, as breeders selected for large body size, such as Pekin, they got white eggs.”

But preference of egg color varies culture to culture. “Another observation is that, in Indonesia, they like blue-green eggs so the Runner ducks have a higher percentage because, my guess is, they were selected for blue-green color when the runners were developed in Southeast Asia.” People who are used to white eggs are enthralled by blue-green eggs. Because of this, John doesn’t work to remove the blue-green genes to create breeds that lay all-white shells.

Metzer Farms has a chart, on their website, to help you decide if you want white-layers or green-layers. Fewer than 2% of their Pekins lay colored eggs. Fawn and white Runners lay 35% colored eggs; Metzer’s black and chocolate Runners lay 70-75% colored. Breed lines from other hatcheries will have different percentages.

Those Crazy Duck Egg Color Genetics

Do you remember high school science classes, where teachers diagrammed those Punnett squares? Yeah, me neither. Genetics get me, every time. So here’s the condensed explanation.

The tendency to lay shells with biliverdin (green shells) and without (white shells) is in the genotype. Green shells (G) are dominant. This means, if the hen has a strong (G) gene, but the drake doesn’t, her ducklings will most likely also have a strong (G) gene.

But this isn’t always the case. Because they’ve been bred so many times, many duck breeds have both (G) and (W) genes, some stronger than others. This would be expressed (Gg) for two green genes, (Gw) for a dominant green gene over recessive white, and (Ww) where the duckling received two white genes with no green gene to overrule.

A Pekin still has some (G) genes, even though the (W) genes are so prevalent they normally win. Once in a while, a duckling female is hatched where the (G) genes shine through, and she grows up to lay green eggs.

Metzer’s chocolate Runners still have a strong (G) gene, though the (W) gene shows up only a third of the time. In their white Runners, the (G) gene shows up in about one of three layers.

How Do I Guarantee Duck Egg Color?

That’s just it. You can’t. Genetic variables such as this are why Easter Egger chickens can lay blue, green, pink, or brown eggs, or why an Olive Egger project isn’t considered successful until the pullet starts laying and her eggs are indeed olive. These genetic variables are also present in ducks.

Says John Metzer, “I had a visitor here from Malaysia and he wanted a high percentage of blue-green eggs, higher than what we had, so we looked at various ways to increase the blue-green percentage.”

By concentrating on specific breeds, you can encourage more of the gene. To get a high amount of blue eggs, first choose ducks that have stronger (G) genetics, such as Metzer’s black or chocolate Runners. Keep hens proven to lay blue eggs and breed them to drakes that come from blue eggs. When those ducklings mature and start laying, keep those that lay blue eggs and breed them to other drakes that come from blue eggs.

Eventually, this dilutes the (W) gene so that it presents less frequently. Of course, you may think you’ve diluted it for good then suddenly a prize hen starts laying …and the egg is white. But that’s part of the fun in chicken eggs vs. duck eggs.

Which is your favorite duck egg color? White, bluish, or green?

Bluish Egg Percentage Data from Metzer Farms

Resources:

Metzer Farms: Breeds of Ducks
The Livestock Conservancy: List of Duck Breeds
Indian Runner Duck Association: Egg Colouration