Understanding Calcium for Chickens: A Complete UK Guide to Strong Shells and Healthy Hens

Calcium is one of the most talked-about nutrients in chicken keeping, yet it’s also one of the most misunderstood. Many keepers know it’s linked to eggshell strength, but fewer understand how calcium actually works inside a hen’s body, how requirements change over time, or how easy it is to cause problems through well-meaning over-supplementation.

This in-depth guide is written specifically for UK chicken keepers. It explains what calcium does, how hens use it, how to spot deficiencies early, and how to support healthy calcium intake safely and legally, without guesswork or unnecessary supplements.

Why calcium matters for chickens – not just for eggshells

Eggshells are the most visible reason calcium matters. A single eggshell is made up of roughly 90% calcium carbonate, and a laying hen needs a steady daily supply to maintain consistent shell quality.

However, calcium’s role goes far beyond eggs. It is essential for skeletal strength, muscle contraction, nerve signalling, and overall metabolic health. Hens that are marginally deficient may continue laying for a time, but the strain shows up elsewhere first, often as brittle bones, fatigue, or reduced resilience during stress periods such as moulting or winter.

Understanding calcium as a whole-body nutrient, rather than just an “eggshell fix”, is key to feeding responsibly.

How calcium works inside a hen’s body

One of the biggest gaps in most calcium advice is explaining how hens actually manage calcium internally.

Laying hens store calcium in a specialised type of bone tissue known as medullary bone. This acts as a temporary reserve that can be drawn on when dietary calcium intake doesn’t perfectly match daily demand, particularly overnight when eggshells are being formed.

If a hen’s diet consistently lacks available calcium, her body compensates by pulling calcium from structural bones instead. Over time, this weakens the skeleton and increases the risk of fractures, even if eggs continue to appear normal for a while.

This is why chronic deficiency is far more damaging than a short-term dip, and why calcium needs to be supplied consistently, not reactively.

Signs of calcium deficiency in chickens

Calcium deficiency rarely appears overnight. It tends to develop gradually, especially in high-producing layers or older hens. Common signs include soft-shelled or thin-shelled eggs, misshapen eggs, or eggs with rough, uneven shells.

In more advanced cases, hens may show signs of weakness, difficulty perching, or reduced mobility. Bone fragility can increase, particularly in the legs and keel bone. Production often drops as the hen’s body prioritises survival over laying.

These signs are explored further in What Do Calci Worms Do for Egg Quality? Stronger Shells Explained (https://syntects.co.uk/what-do-calci-worms-do-for-egg-quality-stronger-shells-explained), which looks at shell formation from a nutritional perspective.

How much calcium do chickens actually need?

Calcium requirements depend heavily on life stage and purpose.

Laying hens typically require a diet containing around 3.5–4% calcium to support regular egg production. This is usually met through a properly formulated layers pellet, which should always form the foundation of the diet.

Pullets that are not yet laying, cockerels, and non-laying birds require far less calcium. Feeding high-calcium diets to birds that don’t need them can cause long-term kidney and metabolic issues. This is why mixed flocks often benefit from calcium being offered separately rather than added universally.

The key principle is that calcium should be available, not forced.

Calcium absorption: the role of vitamin D and balance

Calcium intake alone is not enough. For calcium to be absorbed and used effectively, hens need adequate Vitamin D3. In summer, sunlight exposure supports natural Vitamin D synthesis. In winter, when daylight is limited in the UK, hens rely more heavily on dietary sources.

Calcium also needs to be balanced with phosphorus. Excess phosphorus can interfere with calcium absorption, while severe imbalances can reduce overall bone strength.

This is one reason why throwing multiple supplements into a diet can backfire. Balanced feeding works better than isolated fixes.

Common calcium sources for chickens: benefits and limitations

Most UK layers feeds are designed to meet baseline calcium needs, but additional sources can be helpful during peak laying or for older hens.

Oyster shell grit is commonly used because it breaks down slowly in the gizzard, releasing calcium over time. This makes it particularly useful overnight when eggshell formation is at its peak. It should be offered free-choice rather than mixed into feed.

Crushed eggshells are another option if prepared correctly. They must be thoroughly cleaned, dried, and crushed finely to avoid encouraging egg eating behaviour. Even then, they are best seen as a supplementary source rather than a primary solution.

Live insects can also contribute meaningfully to calcium intake. Live Calci Worms, which are Black Soldier Fly larvae, naturally contain calcium alongside protein and fats, and they align closely with chickens’ natural foraging instincts. Their role as a calcium-supporting treat is discussed in Why Calci Worms Are a Must-Have Superfood for Chickens (https://syntects.co.uk/why-calci-worms-are-a-must-have-superfood-for-chickens).

It’s important to note that in the UK, only live insects are permitted for poultry. Dried insects are not approved for feeding to chickens and should not be used.

Can chickens get too much calcium?

Yes, and this is an area where well-intentioned keepers can run into trouble.

Excess calcium, particularly in birds that are not laying, can place strain on the kidneys and interfere with normal mineral metabolism. Symptoms are often subtle at first and may only become apparent once damage has already occurred.

This is why calcium supplements should never replace a balanced base feed and why “more” is not always better. Responsible feeding is about meeting needs accurately, not maximising intake.

For a broader discussion on moderation and balance, Can You Give Chickens Too Many Treats? Feeding Calci Worms Responsibly offers useful context (https://syntects.co.uk/can-you-give-chickens-too-many-treats-feeding-calci-worms-responsibly).

A practical calcium approach for UK chicken keepers

For most flocks, the safest and most effective approach is simple. Use a high-quality layers feed as the foundation. Offer calcium sources like oyster shell separately so hens can self-regulate. Support absorption through good general nutrition and daylight access where possible.

Use treats, including live insects, as part of enrichment rather than as a substitute for balanced feed. Adjust expectations seasonally, as laying naturally slows in winter and during the moult.

If you’re new to feeding live insects, How to Start Feeding Live Calci Worms: A Simple First Week Routine provides a calm, structured introduction (https://syntects.co.uk/how-to-start-feeding-live-calci-worms-a-simple-first-week-routine).

Calcium done right supports long-term hen health

Calcium is essential, but it works best when it’s part of a wider, thoughtful feeding strategy. Strong shells are a visible benefit, but the real value lies in supporting bone strength, resilience, and long-term welfare.

By understanding how calcium works and avoiding extremes, UK chicken keepers can support healthier hens, steadier laying, and fewer preventable problems over time.