Unexpected Eggshell Color Variance

Reading Time: 4 minutes

What causes odd eggshell color? Discover how eggs are formed inside the hen to shed light on why we get unexpected eggshell colors.

Story and photos by Krislee Johnson

While in the coop doing my morning chores I was met with an unusual surprise.  An unfamiliar colored egg had found its way into one of my nesting boxes.  I was used to seeing nearly every shade of brown from my eight hens but never one with a completely white eggshell.

This discovery lead me on a hunt for more information regarding such a drastic color change.  Was it a result of illness?  Just an oddball egg thing that happens from time to time?  I was determined to comprehend exactly what was going on with one my birds.

Understanding how eggs are formed inside my hen was paramount to my investigation. Get ready to be educated.

Egg Formation

Egg formation starts inside a hen as an oocyte, more commonly known as an egg yolk.  The yolk is formed much the same as human eggs are formed via the act of ovulation in the ovary.

From the ovary the yolk will make its way into the funnel of the ovaduct called the infundibulum.  This is the location where an egg has the opportunity to become fertilized.  The yolk then continues it’s journey into the Magnum where it will pick up the contents of it’s egg white or albumen.

Prior to eggshell formation the yolk and white are carried forward into the Isthmus.  It is in the isthmus where inner and outer shell membranes are created.  This membrane gives the chalazae (the white rope-like strands) something to adhere to for yolk stabilization as well as acting as a foundation for eggshell formation.

The uterus or shell gland is the longest stop in the process of egg creation, totaling nearly 24-26 hours. Calcium is drawn from the hen’s bodily tissues and deposited on the membrane encasing the yolk and albumen.  It is at this late stage an egg receives it’s shell coloring before being laid.

Eggshell Color

Simply put, eggshell coloring is based on genetics. Dependent upon the chicken breed or cross breed, eggs can range from white, to green, to dark brown and every color in between.  While all eggs start out white in color, some results are dependent upon when the eggs are exposed to the pigment.

For instance, Ameraucanas produce oocyanin earlier in the process causing a bluish tint that is apparent throughout the entire shell.  Brown egg layers of various breeds deposit their coloration, caused by protoporphyrin, at the tail end of shell creation.  This results in a shell that is white on the inside and brown on the outside.  Olive Eggers lay eggs having a combination of both pigment methods.  The outcome produces an egg that appears olive green in color.

Causes For Anomalies

Oddities such as my white egg are technically caused by an all-too-brief stay in the uterus during the final phase of shell creation.  This is further supported by the porous feel of my white egg.  While it was hard enough to withstand passing through the vent, the overall integrity does appear slightly compromised.

Stress is the number one cause for most atypical eggs lain by otherwise healthy hens.  Temperature fluctuations, molting and yes, even preliminary stages of minor illness can stress a bird to the point their eggs are affected.

Many young birds under 1 year of age can lay a number of crazy things.  Double or triple yolks, no-shells, wrinkled eggs, no-yolks and other oddities such as my white egg.

Different Types of Anomalies

My early laying hens have expelled blobs of no-shell egg with only thick albumen or tiny eggs during their first month of production.  The gray egg in this photo is a duck egg.

Many of my tiny eggs had either a very small yolk or no yolk at all, as seen in this hard boiled egg.

Dark, wrinkled eggs can be a result of a hen’s system being backed up with too many eggs in the ovaduct.

One of my young girls laid an overly large chicken egg (right), larger than my duck egg (middle) and an average chicken egg (left).

In summary, most eggshell color changes are not a cause for concern unless the situation continues to happen. The same holds true for other misshapen or otherwise abnormal eggs.  If it is ongoing, chances are you should be looking for stressors such as disease or nutritional deficits.  Indicators such as eggshell quality, yolk color and even albumen consistency can give you great insight to the health and condition of your flock.

To learn more about what happens here on the farm and what I’m learning as a first-time flock owner, visit my website Dirt On My Plate.

Originally published in 2016 and regularly vetted for accuracy.