Eggshell Problems: Soft Shells, Thin Shells, and What They Mean

An egg with a rubbery shell or one so thin it cracks in the basket is a message from the hen. The shell is made in the shell gland over many hours, and anything that interrupts that process shows up in the finished egg. Sometimes the cause is simple, and sometimes it points to something worth taking seriously. This guide goes through the main causes and what to do. For background on calcium sources, see oyster shell, limestone and the shell quality question.

What Is Normal?

Occasional odd eggs are common, especially in the first weeks of a pullet's laying life, when her system is still learning the routine. A single soft egg from a hen in the middle of a stressful day does not need a crisis response. Patterns are what matter: several hens, repeated eggs, or a steady worsening.

Common Causes

Several agricultural sources agree on the main list. The Manitoba government's guide to weak-shelled eggs in small flocks and Utah State University Extension's farmer's guide to egg quality cover them.

Age

Both sources note that shell strength declines as hens age, and that very young hens are also more likely to lay thin or soft shells. The Manitoba guide notes that nutritional measures cannot stop age-related weakening but can prevent premature problems, and that shell thickness may improve temporarily during a molt. If your four-year-old hen is laying thinner eggs, that may simply be her age (see the four-year laying curve).

Calcium and Vitamin D

Calcium deficiency is the classic cause. The Utah guide cites 3.5% to 4.0% dietary calcium as a common recommendation for layers, and notes that vitamin D deficiency also leads to thin shells. The Manitoba guide notes that large, pebble-sized particles of limestone or oyster shell last longer in the gizzard and supply calcium overnight, when the shell is being formed, and that insoluble granite grit and ground eggshells are not effective sources. Hens that start laying before they are on a layer diet can deplete bone calcium quickly. Our piece on layer feed, calcium, grit and treats explains how to set this up, and the 10 percent rule explains why too many treats can dilute calcium intake.

The opposite problem exists as well. The Utah guide says excess calcium can cause rough, pimpled shells, so more is not always better. Offer free-choice oyster shell in a separate dish and let the hens decide.

Phosphorus and Other Nutrients

The Manitoba guide notes that excess phosphorus reduces shell thickness, which matters if you mix your own feed, and that insufficient manganese can contribute too. Homemade rations are tricky; see homemade vs commercial feed.

Heat

Both sources list heat stress. Manitoba mentions temperatures above 32 degrees Celsius (about 90 Fahrenheit) as a stress that weakens shells. Hens eat less in heat, so they take in less calcium. Shade, ventilation and cool water help; see summer heat management.

Stress and Crowding

Excitable hens may lay thin or poorly formed shells, and the Utah guide lists stress, overcrowding and rough handling. Predator scares can trigger shell-less eggs. Review your setup in coop size, ventilation and nest boxes. The Manitoba guide also suggests limiting daylight to 16 hours at most, to allow longer uninterrupted rest.

Disease

This is the cause worth worrying about. Infectious bronchitis (IB) attacks the shell gland, and the Manitoba guide notes that it affects unvaccinated birds. The Utah guide says IB can cause misshapen or wrinkled shells and shell discoloration, and that egg drop syndrome causes shell-less eggs. Less common causes include toxins, coccidiosis and infectious laryngotracheitis. If shell problems appear in several hens at once, along with sneezing, rattling, or a drop in production, treat it as a flock-health problem: isolate affected birds and ask a veterinarian. Do not medicate on guesswork. See respiratory disease and when to isolate.

A Practical Troubleshooting Order

1. Is she a new layer or an old hen? Age may be the answer.
2. Check the feed label: is it a layer ration, and is it fresh and not diluted with treats?
3. Is oyster shell available and being eaten?
4. Has it been hot, or has anything frightened the flock?
5. Are several hens affected, or showing signs of respiratory disease?
6. Is she showing other signs, such as straining, lethargy or a swollen abdomen? A hen that lays a soft egg and is straining may be egg-bound; see egg binding and prolapse.

Are the Eggs Safe?

Thin-shelled eggs crack easily, and cracked eggs can admit bacteria. Discard cracked or leaking eggs rather than eating or selling them, and see selling backyard eggs for handling rules.

Be Patient With Fixes

Because a shell takes about a day to form and a dietary correction takes time to work through the hen's reserves, give changes a couple of weeks before judging them. Keep a log, and take photos of odd eggs for the vet. For related reading, farm.fm's food section and the agriculture directory are useful starting points.