Calcium content of 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 hens, quails, turtles, snails, and ostriches. The highest concentrations of calcium carbonate are typically found in ostrich eggshells, but hen eggshells also contain a very high proportion, generally around 95% of the dry shell weight. The remaining shell composition includes small amounts of phosphorus, magnesium, and trace minerals such as sodium, potassium, zinc, manganese, iron, and copper, with phosphorus and magnesium each accounting for about 0.3% of the shell’s content 248.
Dietary Calcium Levels and Egg Mineral Content
The calcium content of eggs and their shells is significantly influenced by the amount of calcium in the laying hen’s diet. Studies show that increasing dietary calcium levels from 2.5% up to 5.5% leads to higher calcium content in the eggs themselves, although the calcium content in the shell may not always increase proportionally. In some cases, the highest dietary calcium resulted in the highest calcium in the egg, but not necessarily in the shell, indicating a complex relationship between dietary intake and mineral deposition 19.
Effects of Calcium Supplementation on Eggshell Quality
Higher dietary calcium levels (up to about 4.5% for hens and 0.5 g/kg for quails) improve eggshell quality, including shell thickness, strength, and overall appearance. However, excessive calcium intake beyond optimal levels can lead to diminishing returns or even negative effects on shell quality and other production parameters. For example, in aged hens and quails, optimal shell quality and egg production were observed at intermediate calcium supplementation levels, while higher levels did not provide additional benefits and could even reduce shell quality 5610.
Factors Affecting Calcium Content and Absorption
The calcium content and quality of eggshells are also affected by factors such as the age and genotype of the bird, housing conditions, and the presence of vitamin D3 in the diet, which is essential for calcium absorption. Prelay diets with higher calcium content improve shell quality throughout the laying cycle, and vitamin D3 supplementation can further enhance calcium utilization and eggshell quality 367.
Eggshell as a Source of Dietary Calcium
Eggshells are a rich and bioavailable source of calcium for human consumption, with about 5.5 grams of calcium carbonate per shell. Techniques such as pulsed electric fields and high-energy milling are being explored to extract calcium from eggshells for use as dietary supplements, offering a sustainable and effective way to meet calcium needs .
Conclusion
Eggshells are predominantly made of calcium carbonate, with their calcium content and quality strongly influenced by the dietary calcium levels provided to laying birds. Optimal dietary calcium improves eggshell strength and thickness, but excessive supplementation can be counterproductive. Eggshells themselves are a valuable source of dietary calcium, and their use as a supplement is supported by their high calcium content and bioavailability.
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