Gail Damerow Discusses Eggshell Imperfections and Anomalies

Alarmed backyard chicken owners report all sorts of shell irregularities in the eggs their hens lay. Continuing our interview series with Gail Damerow, poultry expert and best-selling author, we ask her to discuss eggshell imperfections and anomalies. 

Why are we seeing so many irregularities? 

Chickens have always laid eggs with occasional irregularities. However, industrial egg producers remove eggs with shell imperfections before sending their eggs to market. And they remove from the production line any hen that frequently lays eggs with imperfect shells. Therefore, most people don’t know about shell irregularities until they get chickens of their own.

What causes eggshell imperfections and anomalies?

All sorts of things. Hens experience everyday upsets that can result in an occasional glitch in the system. Or, a hen may have a physically defective shell gland, in which case she will persistently lay eggs with defective shells.

Additionally, there’s always the possibility of an infection in the hen’s ovary or even a flock-wide disease. A fairly common disease that can result in nearly any kind of eggshell irregularity is infectious bronchitis, caused by a coronavirus. This respiratory disease can be hard to detect in mature chickens, except at night when they are on the roost and you can listen for coughing and sneezing.

However, a disease such as infectious bronchitis would cause flock-wide shell anomalies. But most shell irregularities are occasional occurrences that affect individual hens. And they are perfectly normal.

Like fairy eggs?

Precisely. Fairy eggs are small, round eggs that often appear at the beginning of hen’s laying cycle. They may also occur at the end of a cycle, when a hen is about to take time off from laying.

Sometimes a fairy egg contains no yolk. Or, instead of a yolk, it may contain a bit of tissue from the hen’s reproductive system. Nothing to worry about.

Another issue we hear about is thin shells. 

Aging hens often lay eggs with thin shells. That’s because older hens generally lay larger eggs. So the same amount of shell that once covered a smaller egg now covers the larger egg. It just spreads into a thinner layer.

Most eggshells tend to be thicker and stronger in winter, but thinner in warm weather. Hens that feel too hot will pant to cool themselves by evaporating body moisture. Panting can upset the hen’s pH balance, causing a reduction in calcium mobilization. Less available calcium means thinner shells.

Another cause of thin shells is too little calcium in the diet. That shouldn’t be a problem for hens with free-choice access to a calcium supplement such as aragonite.

What causes rough shells? 

Rough shells sometimes result from double ovulation, where the hen’s ovary releases two yolks, one right after the other. So the hen is trying to produce two eggs too close together. As a result, one egg will have no shell and the other will have extra calcium deposits.

Too much calcium in the diet can also result in rough shells. That might be the case when the calcium supplement is added to the layer ration, rather than offered separately free-choice. Hens should have the option to take as much or as little calcium supplement as they need.

What about soft or rubbery shells?

A soft egg actually has a shell, but it’s paper thin so it feels sort of rubbery. Aging hens with reduced calcium reserves may lay eggs with soft shells.

A nutritional deficiency, especially of calcium, can cause soft shells. A laying hen’s calcium needs increase in warm weather and also with age, hence the need for a calcium supplement offered free choice. Soft shells may also result from a diet of stale or moldy feed.

Infrequent soft shells, or soft shells laid during peak production in spring, are nothing to worry about. But persistent soft shells could be a sign of disease, especially if they occur at the same time egg production drops.

How do you explain rigid, wrinkled, or misshapen eggs?

Odd-shaped or wrinkled eggs may occur after a hen has been handled roughly. A shell that’s in the process of being formed could therefore get damaged.

Or weird shapes could result from a double ovulation. If two eggs move through the oviduct close together, the second one will have a thin, wrinkled shell that’s flat toward the pointed end. If it bumps against the first egg, the shell may crack and mend back together in the hen’s shell gland, causing a wrinkle.

Most shell imperfections do not affect the internal quality of the egg, so such eggs are safe to eat. But given the large number of possible eggshell imperfections and anomalies, it’s a wonder that most hens most of the time manage to lay perfectly formed eggs.