The Importance of Crushed Oyster Shells with Laying Hens
- Jan 17, 2025
- 5 min read
Updated: Apr 17
Ensuring the health and productivity of laying hens requires both knowledge and proper nutrition. One of the most important, yet often overlooked, components of a hen’s diet is crushed oyster shell.
(We offer high-quality crushed oyster shell in both 1 kg and 2 kg sizes — ideal for backyard flocks of all sizes.)
This simple supplement can have a significant impact on eggshell strength, egg production, and overall hen health, making it an essential addition for both farmers and backyard chicken keepers.
One of the most common causes of thin or fragile eggshells in backyard flocks is not providing crushed oyster shell as a free-choice calcium source.
What Are Oyster Shells?
Oyster shells are the hardened outer layer of oysters found in marine environments. These shells are primarily composed of calcium carbonate, a critical mineral for many bodily functions in hens—especially egg production.
Oyster shell is typically sold crushed, making it easy for hens to consume when offered free-choice in a separate dish.
(Available in convenient 1 kg and 2 kg bags for small and larger flocks.)
The calcium provided by oyster shell is essential for producing strong eggshells. Thin or fragile eggshells can easily break, which not only reduces usable eggs but can also create sanitation and health concerns within the flock.
Two Sources of Calcium for Laying Hens
Backyard laying hens typically receive calcium from two different sources:
Crushed Limestone
This is the calcium already included in commercially prepared layer feed. It acts as a fast-release source of calcium because the particles are small and quickly absorbed by the hen.
Crushed Oyster Shell
Oyster shell acts as a slow-release source of calcium. The larger pieces remain in the gizzard and are gradually ground down and absorbed over time.
These two sources work together to support the hen’s calcium needs.
Eggshells Are Formed Overnight
Many people assume hens are simply sleeping at night, but an incredible process is taking place.
It takes approximately 25 hours for a hen to produce a single egg, and 18–20 of those hours are spent forming the eggshell. Most of this process happens overnight while the hen is resting.
During this time, a hen can use and replace the calcium in her bloodstream up to 100 times.
This is where oyster shell becomes extremely important. The larger particles sitting in the gizzard slowly dissolve, providing a steady supply of calcium throughout the night when the hen is not actively eating.
The Role of Calcium in Egg Production
Calcium plays an essential role in the life of a laying hen. Hens require approximately 4 grams of calcium per day to maintain proper egg production.
Calcium is primarily used for the formation of strong eggshells. When dietary intake is not sufficient, hens will draw calcium from their bones to meet the demands of laying.
Over time, this can negatively impact bone strength and overall health.
Providing free-choice crushed oyster shell alongside a nutritionally complete layer feed helps ensure hens can access the additional calcium they need for consistent egg production and strong eggshells.
Calcium and Reproductive Function
Calcium is also important for proper muscle function, including the contractions involved in laying an egg.
When hens are under sustained laying pressure, factors such as nutrition, body condition, genetics, and egg size all interact to influence reproductive strain.
In some cases, prolonged stress on the reproductive system may contribute to issues such as prolapse, where internal tissues are pushed outward during laying.
While prolapse is not caused by a single factor, maintaining balanced nutrition—including adequate calcium intake—supports normal laying function, muscle activity, and overall reproductive health.
Offering free-choice oyster shell ensures hens can regulate their calcium intake based on their individual laying demands.
How to Offer Oyster Shell
Free Choice
The best method is to offer crushed oyster shell in a separate dish near the feeder.
This allows hens to consume oyster shell only when they need it, since individual hens have different calcium requirements depending on factors such as age, breed, and how frequently they lay eggs.
Providing oyster shell free-choice allows the hen to regulate her own calcium intake naturally.
(We carry crushed oyster shell in 1 kg and 2 kg options, making it easy to choose the right amount for your flock.)
We also have two different styles of oyster shell dispensers available in our Roslin Recommendations Shop (Amazon Affiliate)
Plastic Wild Bird Feeder - Oyster Shell Dispenser
Benefits of Using Oyster Shell
Stronger Eggshells
The most noticeable benefit is stronger eggshells, which reduces breakage and egg loss.
Better Overall Nutrition
Oyster shells primarily provide calcium but may also contain trace minerals that support overall health and reproductive function.
Cost-Effective
Oyster shells are widely available at poultry feed stores and are an affordable way to support egg production and flock health.
(Our 1 kg and 2 kg options are ideal for backyard keepers looking for convenient, right-sized amounts.)
Improved Bone Health
Adequate calcium intake helps maintain strong bones in laying hens, preventing long-term skeletal problems.
Important Considerations
Quality Matters
Always purchase oyster shell from reputable poultry feed suppliers to ensure the product is clean and free of contaminants.
Individual Hen Needs
Each hen has slightly different calcium requirements. This is why oyster shell should always be offered free-choice rather than mixed into feed.
Skip the Eggshells
Before nutritionally balanced poultry feeds were available, farmers often fed crushed eggshells back to their hens as a calcium source.
Today, this practice is no longer necessary.
Modern layer feed already contains crushed limestone, a quick-release form of calcium. Adding eggshells on top of that provides additional quick-release calcium that hens may not need.
Excess calcium must be filtered through the kidneys, which can place unnecessary strain on the hen’s kidneys.
For this reason, oyster shell remains the safer supplemental calcium source.
Additional Support for Eggshell Quality
If needed, we also provide a supplement to support healthy eggshell production.
• Supports musculoskeletal integrity
• Promotes good bone structure
• Supports healthy eggshell formation
• Helps with calcium and phosphorus metabolism
• Provides 400 IU Vitamin D3 per 5 ml (1 teaspoon)
• Source of additional calcium
When would this be used?
While free-choice oyster shell should always be the primary calcium source, additional support may be helpful in specific situations:
Hens laying thin or fragile shells despite access to oyster shell
Older hens with reduced calcium absorption
Periods of peak egg production
Times of stress or recovery
Chick' N Calcium helps support calcium absorption and utilization, but it should always be used alongside a nutritionally complete layer feed and free-choice oyster shell — not as a replacement.
Crushed Oyster Shell for Laying Hens
We offer high-quality crushed oyster shell in two convenient sizes:
Conclusion
For anyone keeping laying hens, crushed oyster shell is an essential part of proper flock nutrition.
From producing strong eggshells to supporting bone health, oyster shell provides the slow-release calcium hens need during the long overnight process of eggshell formation.
By offering oyster shell free-choice alongside a quality layer feed, backyard chicken keepers can help ensure their hens remain healthy, productive, and thriving.
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