Calcium content in eggs
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Calcium Content in Eggshells: Composition and Variability
Eggshells are primarily composed of calcium carbonate (CaCO3), making up about 84% to 98% of the shell’s weight across various species, including chickens, quails, ostriches, turtles, and snails 38. In chicken eggs, the dry eggshell typically contains around 95% calcium carbonate, with the remainder consisting of small amounts of phosphorus, magnesium, and trace minerals such as sodium, potassium, zinc, manganese, iron, and copper . The actual calcium content in eggshells can be measured using chemical analysis methods like titration, which have shown that eggshells contain about 0.025 grams of calcium per shell, with CaCO3 content theoretically reaching up to 98.43% .
Dietary Calcium Levels and Their Impact on Egg and Eggshell Calcium
The amount of calcium in a hen’s diet directly affects the calcium content and quality of both the egg and its shell. Studies have shown that increasing dietary calcium levels in laying hens improves eggshell strength, thickness, and overall quality, especially in older birds 124569. For example, feeding hens diets with calcium levels ranging from 3.5% to 4.7% led to stronger and thicker eggshells, with fewer cracked eggs and improved shell appearance 4569. However, excessively high calcium intake (above 4.2 g per bird per day) may not provide additional benefits and can even reduce shell quality or increase mineral accumulation in organs like the kidneys .
Calcium in Egg Content and Human Nutrition
While most of the calcium in an egg is found in the shell, the egg’s edible parts (yolk and white) also contain small amounts of calcium. The mineral content of the egg itself can be influenced by the hen’s diet, with higher dietary calcium leading to increased calcium levels in the egg . This is important for human nutrition, as eggs can contribute to dietary calcium intake, though the majority of calcium is in the shell, which is not typically consumed unless processed as a supplement .
Factors Affecting Eggshell Calcium Content
Several factors influence the calcium content and quality of eggshells, including:
- Dietary calcium and vitamin D3: Both are essential for optimal calcium absorption and eggshell formation. Vitamin D3 enhances calcium uptake, and their combined supplementation improves egg production and shell quality 259.
- Age and genetics of the bird: Older hens and different breeds may require higher dietary calcium to maintain shell quality 456.
- Prelay diet: Feeding higher calcium diets before the onset of laying improves shell quality throughout the laying cycle .
- Form of calcium supplement: New forms like calcium pidolate can improve calcium absorption and eggshell quality in aged birds, with optimal effects at specific concentrations .
Eggshell Calcium as a Supplement
Eggshells are a rich, natural source of calcium carbonate and can be processed for use as a dietary calcium supplement for humans. Techniques such as pulsed electric fields and high-energy milling are being explored to extract calcium from eggshells efficiently . Eggshell-derived calcium is considered bioavailable and can be a valuable supplement, especially when combined with vitamin D to enhance absorption .
Conclusion
Eggshells are predominantly made of calcium carbonate, with calcium content ranging from 84% to 98% depending on the species. The calcium content and quality of eggshells are strongly influenced by the dietary calcium and vitamin D3 levels provided to laying hens. Optimizing these dietary factors not only improves eggshell quality and egg production but also enhances the nutritional value of eggs for human consumption. Eggshells themselves can serve as an effective calcium supplement when properly processed.
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