Genetic Variation in Shell Strength and Its Relationship to Egg Size

Abstract

Approximately 13,300 eggs from 575 Single Comb White Leghorn (SCWL) hens from 20 sire families were evaluated for variation in shell strength and egg weight and the relationship between strength and weight. Nondestructive deformation was used to assess shell strength from onset of lay dirough 77 weeks of age. Additional assessments of shell strength by breaking strength and percent shell were made at 41, 60, 68, and 77 weeks of age.The values for shell strength and egg weight were erratic for the first 7 weeks of lay. Heritabilities for egg weight ranged from .32 ± .10 to .45 ± .16 with the highest estimates obtained during the period of 31 to 37 weeks of age. The range of heritabilities for deformation was .18 ± .09 to .38 ± .11 with the highest estimates also occurring during the 31 to 37 weeks of age period.Differences between sire families in deformation during the period of selection (31 to 37 weeks of age) were present through the 77-week test period. The low-shell-strength families showed a decrease in shell strength at an earlier age than the high-strength families.Phenotypic correlations between egg weight and shell deformation were near zero, whereas frenetic correlations of these variables ranged from −.29 to −.57. These correlations indicate that selection for shell deformation would not have a deleterious effect on egg weight.