A soft shell, or rubber, egg looks very much like a small water balloon. Causes range from nutrition issues to disease. Credit: Courtesy of Mariah Darling

There is nothing quite like reaching under a laying hen expecting to pull out a fresh egg and instead ending up with something that looks and feels like a tiny water balloon. This is referred to as a soft-shelled or rubber egg.

A soft-shelled egg is one where the yolk and white is covered by a thin, soft membrane instead of a hard shell. In some cases a shell may be there, but it’s very thin and cracks at the slightest touch.

According to Dr. Anne Lichtenwalner, director of the University of Maine Veterinary Diagnostic Laboratory, there are three main causes of soft-shell eggs — nutrition, stress and disease.

Laying hens require up to four-times more calcium to form hard shells than non-layers, so you need to provide calcium supplements in addition to their regular feed. Lichthenwalner suggests using oyster shell grit and feed formulated specifically for laying hens.

“Layer diets should have Vitamin D,” Lichtenwalner said. “And a small amount of fat so they can absorb [the calcium].”

A stressed-out or nervous chicken may also lay soft shelled eggs.

“Make sure hens have a secure place to lay without being disturbed,” Lichtenwalner said. “Nervous or frightened birds may change the rate of passage of eggs through the oviduct which could impede shell maturation.”

That safe and secure place should also have plenty of natural light, she said.

Finally, if your chickens are on a good diet, have a safe place to lay their egg and you are finding soft-shell eggs, you may have to consider disease.

“Some diseases may manifest by causing egg abnormalities,” Lichtenwalner said. “There are usually other signs such as diarrhea or possibly death.”

Among the diseases that can cause soft shell eggs in your chickens are infectious bronchitis, Newcastle disease, avian pneumovirus and avian influenza.

If you suspect the soft shells are caused by a disease, Lichtenwalner urges you to contact the Maine state veterinarian at the Maine Department of Agriculture, Conservation and Forestry or the University of Maine Veterinary Diagnostic Laboratory. They can perform necropsy on dead birds to confirm the presence of any diseases or consult with what may be wrong with a sick chicken.

As for the soft shell egg: don’t eat it. The job of an egg shell is to protect the inside of the egg. A soft shell can allow bacteria to pass through that gelatinous outer membrane and contaminate the egg which can make you sick if consumed.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.