Why Some Eggs Have Stronger Shells: The Science Behind Egg Quality
Nov 25, 2025 • Egg Facts • 7 minute read
Not all eggs are created equal. Some have thick, strong shells while others crack with the slightest pressure. But what causes these differences? From genetics to nutrition and environmental factors, several elements influence shell strength. In this article, we break down the science behind egg quality and how you can support your hens in laying healthier eggs.
What Determines Shell Strength?
Eggshells are primarily made of calcium carbonate, a mineral structure that forms during the last few hours of the egg’s journey through the hen’s oviduct.
The strength of this shell depends on both the amount of calcium available and how efficiently the hen’s body deposits it.
Young, healthy hens with balanced diets tend to produce eggs with stronger, more resilient shells.
How Nutrition Impacts Egg Quality
Calcium is the most important nutrient for shell formation. Hens that lack dietary calcium often produce thin or soft-shelled eggs.
Other nutrients—such as vitamin D3, phosphorus, and essential amino acids—support proper calcium absorption and overall egg development.
The Role of Genetics and Breed Differences
Some chicken breeds naturally lay eggs with stronger shells. Heritage breeds and certain dual-purpose hens often outperform high-production layers in shell quality.
Genetic factors influence how efficiently a hen processes minerals and how much calcium her body stores for egg production.
Older hens may experience a gradual decline in shell quality as their calcium reserves weaken over time.
Environmental Factors That Affect Shell Strength
Stress, extreme temperatures, and poor coop conditions can disrupt a hen’s laying cycle and weaken eggshell development.
Proper lighting, clean housing, and consistent routines help hens maintain a healthy laying rhythm.
How to Encourage Stronger Eggshells
Provide a constant supply of high-quality layer feed formulated with the right balance of calcium and protein.
Offer supplemental calcium sources such as oyster shell or crushed, baked eggshells in a separate dish.
Ensure your hens get enough sunlight or vitamin D3, which is essential for calcium absorption.
Reduce stress by keeping the coop clean, dry, and well-ventilated, and by giving hens enough space to move comfortably.
Conclusion: Healthier Hens Lay Better Eggs
Strong eggshells start with healthy hens. By supporting your flock with proper nutrition, good housing, and low-stress conditions, you can significantly improve egg quality.
Understanding the science behind eggshell formation empowers you to create an environment where your hens can thrive and produce the best eggs possible.
