Eggs Genetics

Feeling Blue Over Fading Eggs

You’re probably wondering what dogs have to do with chickens – if you hold on for a moment I’ll try to make the link.

I’ve had three Standard Poodles in the last 15 years, all different colours: apricot, red and parti-coloured chocolate and white. All started out with beautiful, vibrant colours and faded as they aged. I’m not sure if this is a trait specific to poodles, but it turns out that there’s a dilute gene causing their colours to fade. Unfortunately it’s a dominant gene, which makes it so common.

If you’re really concerned about your dog’s colour ‘holding’ then you’d need to find offspring from two parents that don’t carry the gene. If their colours are still strong by the age of two there’s a good chance they’re not carriers.

So what’s all that got to do with chickens? Genetics, of course. The segue is that eggshell colour can fade over time too.

When I posted photos of my best blue and olive eggs on several online forums I received over 1000 likes, reactions and comments. Longtime breeders said they’d kill for eggs with that depth of colour. Someone else said they’d cry. I was overwhelmed by the response, because really they were a happy accident. I can’t take any real credit except for choosing the birds I have and hatching their eggs.

Many breeders with purebreds work towards their Standard of Perfection. Genetics is often a crapshoot, especially when working with crosses, which most of my birds are. It takes successive generations to figure out what some of the genes that a chicken carries, sometimes waiting until they are expressed in their offspring. And that takes time.

It turns out some of those phenomenal blues have gone the way of my poodles, fading to wishy-washy, nondescript blue. Such a disappointment.

I’ve done a bit of online research, waded through some scientific journal articles (that I barely understood) and have come up with some explanations for what might be going on with my eggs.

Despite a relatively small palette of compounds bird eggshells display a wide range of colours. All that variation is a result of just two ancient pigments. While the genetic and biochemical workings are not fully understood it’s believed that protoporphyrin, which is linked to the heme molecule (red blood cell) creates the red-brown colour and biliverdin, a by-product of hemoglobin breakdown, contributes to the blue egg shell.

So what causes blue eggshells to fade over time?

  • The movement of biliverdin into the shell gland and oviduct is regulated by estrogen. An aging hen’s decreasing estrogen affects the biliverdin.
  • Biliverdin is an antioxidant. Aging, bacterial and viral loads can create a need for it elsewhere, so it gets diverted from egg shell production.
  • Pigment that is used in eggshell colour is also required for leg, feather and comb colour. Molting not only uses more protein, but also more pigment.
  • The overall amount of pigment can remain relatively stable, but the size of eggs, and therefore the area of eggshells, increase as a hen gets older. In short, the same amount of pigment has to cover more mass.
  • And then there’s genetics: the genes that hens inherit from their parents affect the intensity and longevity of eggshell colour.

Some folks say that their brown eggs fade as well. I haven’t found that to be as common, or as significant, as with the blues.

I guess this means if you have a beautifully coloured dog, or a chicken egg, enjoy it while you can. Depending on what genetics, and other issues, are at play that colour might not last.

All Photos: Bitchin’ Chickens   Featured Image Credit: Ameraucana Breeders’ Club

3 comments on “Feeling Blue Over Fading Eggs

  1. The egg color does come back every year just as strong after a moult.


    • I haven’t figured out which hens are laying some of those eggs so haven’t been able to keep track of their molts. Most of them seem to molt around the same time. Molting is only one factor that affects egg colour, but I am hoping some of those blues return.


  2. Thanks! I had no clue to the fading phenomena in dogs and eggs! I always enjoy your writing, but it was so nice to read something in the morning that made my brain wake up up with a “huh? What’s this?!!” reaction. 🙂

    Liked by 1 person

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Everything You Need To Know About Small Flock Chickens & More

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