Abstract
ABSTRACT This experiment was conducted to evaluate the effect of egg weight and egg physical characteristics on embryonic development, hatchability, and hatchling weight of Japanese quails (Coturnix coturnix japonica). In total, 689 eggs were classified in two categories: small (<13.5 g) or large (≥13.5 g), and different external eggshell and internal quality traits were measured. On days 6 and 14 of incubation, tissue triiodothyronine (T3) and thyroxine (T4) were extracted from embryos in both egg sizes and analyzed. Relative to internal egg-quality traits, large eggs had significantly higher yolk height, yolk diameter, yolk weight, albumen height, and albumen weight than small eggs (p≤0.01). However, Haugh unit score (p=0.27) was not significantly different between the two egg sizes. Relative to eggshell quality parameters, large eggs had significantly higher total pore count, surface area, eggshell volume, and eggshell weight than small eggs (p≤0.05), with consequent higher hatchability rate and hatchling weight. Pearson’s correlation coefficients revealed significant correlations (p≤0.05) between egg weight and different external and internal egg quality parameters. Thyroid hormone levels were not significantly different between egg groups on d 6 day, while on d 14, a significant difference was recorded (p≤0.05). In conclusion, larger egg sizes are recommended to obtain better hatchability, lower embryonic death rates, and heavier hatchlings compared with smaller eggs of Japanese quails.