Eggshell of birds, as a natural shield and package, protects the tissues inside it from microbial and mechanical damages. Proper intake of calcium, as an important and effective factor in increasing the strength and quality of the eggshell could reduce complications. In this paper, the effect of dietary calcium at five different levels on engineering features of Japanese quail eggs in a mother quail herd in their first laying period was investigated. The values for average of mass, volume, specific mass, shell thickness, major diameter, central diameter and rupture force along the longitudinal and transverse axes were measured. Rupture energy or toughness, slope of the rupture curve (hardness), deformation along longitudinal and transverse axis to the point of rupture as well as longitudinal and transverse deformation of 450 tested quail eggs were measured. The characters of specific mass, shell thickness, rupture force, and slope of rupture curve of quail eggs indicate the strength of quail egg. In this study, variations in all parameters indicating shell strength at different levels of dietary calcium were consistent with each other. By increasing the calcium content of the quail diet from 1.5 to 3 wt%, the volume and weight of quail eggs dropped and shell thickness was reinforced. According to the results, the shell strength of quail eggs along the transverse axis is slightly less than the longitudinal axis, but the flexibility and energy required for quail egg rupture are much greater across the longitudinal axis.

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