Relationship of eggshell ultrastructure and shell strength to the soundness of shell eggs

Factors affecting the soundness of shell eggs are of primary concern to egg processors due to substantial financial losses from cracked and leaker eggs. Ultrastructural analyses were used to examine the palisade layer width and mammillary knob layer thickness of sound, cracked, and leaker eggshells. Subjective observations were also made. There was no significant difference (P > 0.05) in the width of the palisade layer or the mammillary knob layer among sound, cracked, and leaker eggshells. The eggshell strengths of sound, cracked, and leaker eggs were evaluated using puncture force and shell thickness measurements. Sound eggshells were found to have a significantly (P < 0.05) higher mean puncture force (35.3 N) than cracked (30.4 N) and leaker (28.4 N) eggshells. The mean puncture force values for cracked and leaker eggshells were not significantly different from each other (P > 0.05). Regression and correlation analyses indicated a significant correlation (P < 0.01; r = 0.61) between palisade layer width and puncture force. The mean shell thickness values for cracked (0.36 mm) and leaker (0.35 mm) eggs were significantly lower (P < 0.05) than those of sound eggs (0.38 mm), although cracked and leaker eggshell thickness did not differ significantly (P > 0.05). The correlation coefficient between puncture force and shell thickness was significant (P < 0.01; r = 0.56), indicating a possible relationship.