Kim’s Korner: Finding the Right Angle: Earlobes and Eggshells
By: Dr. Kimberly Vonnahme
If I have heard it once, I have heard it hundreds of times…. Eggs with brown shells are healthier than those with a white shell. As an animal scientist, I use this statement as an opportunity to help educate why we shouldn’t judge a book by its cover—or in this case, an egg by its shell color.
The color of the eggshell is simply determined by the genetics of the hen, and we can predict the color of the eggshell by the color of the hen’s earlobe color.
WHAT?! Chickens don’t have ears! Oh—but they do!
Generally, hens with white earlobes will produce white eggs, and those with pink or red earlobes will lay brown eggs. But all eggs start out white because the shells are made from calcium carbonate. If you crack open a brown egg, you will often find that the inside of the shell is white.
There are hens that can lay blue and green eggs, but earlobe color doesn’t appear to be a predictor for these birds. And if you look inside a blue colored egg, you will notice the blue color goes through into the inside side of the shell. Eggs-iting, isn’t it?!
Nature has its own way of coloring eggs, and it doesn’t require boiling water or food coloring like we use at Easter. Let’s eggs-plore how this happens!
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. A chicken yolk, or ovum, forms in the hen’s ovaries. A fully formed yolk leaves the ovary, is picked up by the oviduct, and starts a five-stage process to help ensure the yolk makes it safely to the outside world. The entire egg-forming process can take a little more than 24 hours.
In the fourth and longest stage, the outer shell is laid down. At that time, there are pigments that can be deposited onto the shell, producing its color. Calcium carbonate is the main “ingredient” of the eggshell, and it is white. If you are a hen that lays brown eggs, you will produce a pigment (protoporphyrin) that is deposited onto the shell.
This happens late in the process of shell formation, so this is why the inside of the egg is still white. If you are a hen that lays blue eggs, you have the pigment called oocyanin, which penetrates both the exterior and interior of the shell. In hens that lay green eggs, they produce oocyanin, but also have the pigment protoporphyrin, thus the brown exterior turns the blue to a green looking color.
Have you ever seen a speckled egg? The theory is that speckles on speckled eggs are just extra calcium deposits, or that there is some disturbance during the process when the shell is being laid down. There is nothing different about the egg on the inside, though, so don’t worry about not including it in your breakfast!
While a hen will lay the same-colored egg throughout her lifetime, sometimes the color may appear slightly darker or lighter due to the hen’s age, her diet, and her stress level.
So if you are gathering eggs from a group of hens that have different genetic backgrounds, but they are all being fed the same diet, the nutritional value of the eggs will be similar regardless if they have white, brown, blue, or green shells. Finding different colored eggs is such a fun and delightful thing to observe! I love that nature gives us diversity in the things we are surrounded by!