Shell Structure and Composition of Poultry Eggs

  Objective   Shell structure and composition of eggs laid by different kinds of poultry were compared.

  Method  Thirty eggs of Jiangnan white geese, Rugao yellow chickens, and Jinding ducks were examined for microstructures of the inner/outer surfaces and cross-sections of fragments from various parts under a scanning electron microscope, determined on the physical properties using a strength tester, measured for the thickness with a spiral micrometer, and analyzed on the chemical composition by standard methods.

  Result   The egg weight, shell weight, and shell thickness of different species of poultry differed significantly (P＜0.05) with a ranking of goose eggs＞duck eggs＞chicken eggs. The shell strength, shape index, and weight ratio of the goose eggs were significantly higher than those of the chicken or duck eggs (P＜0.05). Both thickness and proportion of palisade layer of goose eggshell were significantly greater than those of chicken or duck eggshell (P＜0.05). The transverse section density and integrality of goose eggshells were better and the mastoid layer more closely related to the shell layer, while the shell strength highly correlated with the effective layer thickness showing a correlation coefficient of 0.603. The relative contents of carbon, oxygen, calcium, and zinc in the eggshells did not differ significantly (P＞0.05), and oxygen, calcium, and carbon were the greatest amount of inorganic substance and present mainly in the form of calcium carbonate. Thus, the eggshell quality did not depend on the relative content of these elements.

  Conclusion   Goose eggs are significantly different from chicken eggs and duck eggs in terms of shell strength, shell thickness and shell structure. The eggshell strength does not depend on the relative content of the elements, but is more affected by the ultrastructure of the eggshell, and the density of the eggshell directly affects the eggshell strength.