What Can You Tell From An Eggshell?

Poor health, dietary problems and even physical differences can affect eggshell texture, thickness and more, so pay attention to what your hens lay.

by Susan Brackney
PHOTO: Susan Brackney

Over the years, most of my hens have laid perfectly respectable eggs, complete with smooth, hard shells. But a couple of them have produced eggs with oddly textured surfaces. In the case of one particular hen, every egg she lays includes the same pronounced ridge. And, once in a great while I’ve found egg-like “water balloons”—eggs missing their shells entirely.

Of course, it takes time and a lot of energy to make a proper egg. Plenty of things can go wrong along the way. While some eggshell anomalies are no big deal, others may indicate a problem with your hens’ health, diet or environment.

Eggs 101

“The egg is really an amazing thing,” University of Florida College of Veterinary Medicine professor Gary Butcher says. “From the time the hen releases the yolk until the egg is laid is about 25 hours.”

After a hen releases a yolk from her ovary, she adds the egg white in a portion of her oviduct called the magnum. Next, it enters the isthmus. This is where the inner and outer shell membranes are placed around the yolk.

The egg’s last stop is the uterus or shell gland.

“This is where she spends about 20 to 23 hours putting on the outer shell,” Butcher says. “So, if you ever see an egg that’s laid without a shell, you’ll see these two membranes around it. They’ll be rubbery or leathery with no shell.

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“That means the hen released her egg at this stage before she could put the shell on.”

Read more: You may find one or more of these odd eggs in the laying box!

Too Many Treats?

According to Butcher’s work “Concepts of Eggshell Quality,” eggshells typically contain a little over two grams of calcium, and most laying hens need at least four grams of calcium each day.

Eggshells are also made up of phosphorus, magnesium and trace amounts of sodium, potassium, zinc, manganese, iron and copper. A lack of essential nutrients—especially calcium—is one of the most common causes of missing or flawed eggshells.

“A lot of people kill their chickens with kindness, so to speak,” Butcher explains. “People may have bags of commercial layer feed, but they’ll also throw in all kinds of treats. And, just like any little kid, if you give the kid a choice of eating a good, nutritional plate of food or put a bunch of treats around, he’s going to eat all of the treats.”

Offering goodies like cracked corn and mealworms occasionally is great—just don’t let your chickens overindulge. “If they fill up on these, then they’ll be nutrient-deficient,” he continues. “This leads to problems with eggshells, egg size and things like that.”

Summer Heat

Chickens’ appetites also may wane during hot summer days. This, in turn, can affect their overall egg production and their eggshells.

“If they really cut back on how much they eat and they’re not getting what they need, you’re going to pretty quickly see eggshell weaknesses,” Butcher says. “You’re also going to see egg size get smaller, because they’re not getting the protein, which makes [eggs] bigger. And they’re not getting the calcium, which makes the shell better.”

Rough Shells

I have one beloved, ancient hen who still lays eggs—many of which are rough-shelled. “She’s in the process of putting on the shell, she doesn’t finish it, and she releases it too early,” Butcher says. “So, the eggshell is thin, and it isn’t smoothed over.”

(If the old gal kept her egg in the shell gland for another six to eight hours, it would probably come out looking just fine.)

As for younger hens laying eggs with rough or bumpy shells, make sure they’re getting complete nutrition. You should also supplement their calcium as needed.

If an entire flock’s eggshells look rough? That’s cause for extra concern. Check them for infectious bronchitis, Newcastle disease or other serious health issues.

Read more: Infectious bronchitis is a concerning coronavirus for poultry.

‘Body Checks’

What about eggshells with distinct lines or ridges? Not to worry. Odds are these eggs were damaged—and subsequently repaired—during shell formation.

“We call that a ‘body check,’” Butcher says. “When the hen is forming the shells inside of her uterus, the eggshell may get a fracture in it. Then she basically continues to produce shell around it and covers over that crack.”

He adds, “If the hen is laying an egg every day with the same mark on it, a second possibility would be that she has a scar. This was an injury in the uterus where she healed over it with a scar. So, where that egg is in contact with that scar, the shell is not being put on it, like other places.”

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