We studied the correlations between egg geometrical parameters (i.e., egg shape index, sphericity, geometric mean diameter, surface area, and volume) and eggshell qualities, or the organic matrix in eggshell. Eggs were collected from 5 poultry breeds belonging to 3 species (commercial Hy-line Brown Chicken, Shaoxing Duck, Jinding Duck, Taihu Goose, and Zhedong White Goose). The geometrical parameters showed high variation among 3 species of poultry, and even between breeds in the same species. The five geometrical parameters were grouped into 2 sets, one contained shape index and sphericity, the other comprised geometric mean diameter, surface area, and volume. The parameters in the same set can be perfectly fitted to one another. Egg weight, shell membrane weight, and calcified shell weight were significantly correlated with geometric mean diameter, surface area, and volume. In accordance with false discovery rate-adjusted P value, both shell membrane relative weight and calcified shell thickness showed no significant correlations with any of the geometrical parameters. However, the correlations between geometrical parameters and other shell variables (calcified shell weight, shell relative weight, calcified shell thickness uniformity, and eggshell breaking strength) depend on breed. Both constitutive proportions and percentage contents of 3 eggshell matrix components (acid-insoluble, water-insoluble, and both acid and water facultative-soluble matrix) had no effects on egg shape and size. The correlations between the amounts of various shell matrix, egg shape and size depend on breed or species. This study provides a methodology and the correlation between geometrical parameters and eggshell qualities, and between geometrical parameters and organic matrix components in calcified shells.
Keywords: egg; eggshell matrix; eggshell quality; geometrical parameter.
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