This experiment was designed to study the relationship between mechanical properties and ultrastructure of three genetic groups (Fayoumi, Gimieizah and Brown Hy-Line strains). To assess eggshell mechanical parameters a total of 120 eggs from each strain was used. This study suggested predicting the mechanical properties and ultrastructure of eggshells when egg weight was equal for the three strains (39.8 g). There was a significant difference among strains for shell thickness, eggshell breaking strength and stiffness, with the Fayoumi eggshells recording the highest values compared with other strains. The palisade layer of Gimieizah and Brown Hy-Line eggshells was thinner than that of Fayoumi eggshells. There were significant correlations between palisade length and breaking strength (0.51), shell thickness (0.89) and stiffness (0.48); however, the length of the palisade layer was significantly negatively correlated with elasticity (–0.85). The Fayoumi (local Egyptian strain) showed higher resistance for eggshell breakage than the Hy-Line commercial strain due to their longer palisade layer noting that there were no significant differences in egg weight between the two. The length of the palisade layer plays an important role in eggshell strength, so it is of interest to include these parameters in selection programs aimed to improve eggshell strength. However, a negative correlation between length of palisade layer and elasticity prevented improvement of these two parameters.
An experiment was conducted to evaluate egg quality and ultrastuctural measurements of eggshell using a Scanning Electron Microscope (SEM) in 2 lines (selected and control) of Japanese quail. A selection program was applied over 22 consecutive generations for higher egg production and lower broken egg percentage. The results revealed that the females of the selected line produced significantly (P < 0.01) higher egg mass compared to that of the control line. Also, the selection procedure significantly improved feed conversion ratio. The eggshells of the selected line had a higher breaking strength compared to those of the control line, although there was no difference between them in shell thickness. Significantly higher wet (P < 0.01) and dry (P < 0.05) eggshell percentages were found in the selected line. In general, the eggshells of the selected line had a lower total score (good) of ultrastructural evaluation compared to the control line. According to scanning electron microscope data, the incidence of certain structural variants was more common in eggshells of the control line suggesting poor shell strength. The incidence of alignment was more prevalent in control eggshells compared to selected ones, suggesting lower resistance to breakage. Late fusion and large interstitial spaces of the palisade layer indicating decreased resistance to fracture were observed in control eggshells. It could be concluded that the improvement eggshell quality may be caused by the long-term selection for lower cracked and broken egg rates from generation to generation.
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