The Relationship of Age, Method of Measuring, and Strain on Variation in Shell Strength

Abstract

The shell strength of three commercial brown egg and three commercial white egg strains was assessed by specific gravity, deformation, breaking strength, and thickness for 17 months of production. Correlations between shell strength measures and egg weight were determined. The relative magnitude of the contribution of various egg characteristics and age to variation in deformation and breaking strength was determined by stepwise multiple regression analysis.Differences between strains were consistent for methods of assessing shell strength. Although the mean shell strength of the brown egg strains was lower than that of the white egg strains, differences depended on which strain comparisons were made.Correlations among different measures of shell strength were highly significant for all comparisons. No significant correlations of egg weight or width/length ratio with other variables were observed. Differences in magnitude of correlations in these strains were small, and there were no trends to differences with age or different methods of assessing shell strength.Shell thickness accounted for the most variability in deformation whereas specific gravity accounted for the most variability in breaking strength. Alternatively, specific gravity and thickness contributed significantly to the variability of deformation and breaking strength, respectively. Age and width/length ratio were more important in accounting for variability in breaking strength than in deformation. No consistent trends in the accounting of variability within deformation or breaking strength were apparent between strains or ages. However, less of the variation in the brown-egg strains could be accounted for by the variables regressed.