Eggshell formation: the science behind a stronger shell
Research on eggshell formation: calcification mechanisms, factors of strength, and ways to improve egg quality in poultry farming.
Forming an eggshell is a fascinating biological process that ensures the egg remains intact, allowing proper embryo development. This intricate process unfolds within the hen and is influenced by biological mechanisms and external conditions. A durable eggshell minimizes the risk of breakage, facilitates gas exchange, and provides a secure environment for the developing chick. Understanding the mechanics of shell formation and the factors that affect its strength is essential for optimizing egg quality and minimizing production losses.
How an eggshell forms
An eggshell is not just a simple outer layer — it is a carefully structured, multi-layered formation that takes over 24 hours to complete. The most crucial phase, calcification, spans approximately 20 hours and defines the shell's strength. The process initiates with calcium deposits on the egg membrane, forming the foundation for a growing mineral network. As layers of calcium accumulate, they create a rigid yet porous structure, allowing oxygen exchange while maintaining protection. The final step in shell formation is the application of the cuticle, a thin protective coating that shields the egg from bacteria and environmental contaminants.
Factors that determine shell strength
An eggshell's resilience is shaped by various factors, including diet, environmental conditions, and the hen's overall health.
1. Balanced Nutrition
  1. Each egg requires approximately 2.2–2.3 grams of calcium for shell formation.
  2. Since a hen absorbs only about 60% of calcium from its diet, feed should contain a minimum of 4% calcium.
  3. A blend of fine and coarse calcium sources ensures steady absorption throughout the day.
  4. Calcium consumption is most effective in the evening, as most shell formation occurs at night.
2. Hen's Age and Productivity
  1. As hens age, they tend to lay larger eggs, which can lead to thinner shells.
  2. Post-molt, egg quality often improves as the reproductive system regenerates.
3. Impact of Heat and Environment
  1. High temperatures cause hens to consume less feed, reducing calcium intake.
  2. Increased respiration due to heat alters blood chemistry, negatively affecting calcium absorption.
  3. Supplementing drinking water with sodium bicarbonate and vitamin C can help mitigate these effects.
4. Health and Stress Management
  1. Diseases such as infectious bronchitis and mycoplasmosis can weaken the shell by interfering with the reproductive system.
  2. Stressors like sudden environmental changes or poor management can disrupt calcium absorption and even impact shell pigmentation.
What determines shell color?
Several elements contribute to variations in eggshell color, including:
  1. Genetics: Determines whether a hen produces white, brown, or blue eggs.
  2. Egg Production Rate: Hens that lay more frequently tend to produce lighter-colored eggs.
  3. Aging Process: Eggshells naturally fade as hens grow older.
  4. Diet and Medications: Some nutritional deficiencies or medications (such as nicarbazin) can alter shell pigmentation.
  5. Environmental Stressors: Changes in egg-laying timing or stress can impact shell color consistency.
Certain breeds, like Marans, are known for maintaining deep brown shells even with high production levels.
Ensuring a stronger eggshell
To enhance eggshell durability and reduce breakage:
  • Provide a diet rich in calcium, phosphorus, and vitamin D3.
  • Schedule calcium intake for the rest of the day to support nighttime shell formation.
  • Implement strategies to protect hens from extreme temperatures and stressors.
  • Monitor flock health and apply proactive disease prevention.
  • Adjust nutritional plans for aging hens to maintain eggshell integrity.
A well-formed eggshell result from proper nutrition, environmental balance, and overall flock health. Farmers can achieve better egg quality, minimize breakage, and improve overall productivity by carefully managing these elements.
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