HERITABILITIES AND CORRELATIONS FOR EGG-SHELL CRACK FREQUENCY, BODY CHECKING, EGG NUMBER AND EGG WEIGHT IN LAYING HENS

1. Egg shell cracks and body checking were assessed on a total of 25 776 eggs collected from 744 hens of two selected White Leghorn strains between 65 and 72 weeks of age. 2. The sire-component heritabilities in the two Strains, respectively, were 0.59 +/- 0.23 and 0.36 +/- 0.20 for total cracks and 0.41 +/- 0.20 and 0.49 +/- 0.22 for body checking. The heritabilities for hole, star and hair cracks ranged from -0.03 +/- 0.13 to 0.66 +/- 0.24. 3. The frequency of total cracks did not bear any significant antagonistic relationship with body checking, egg number and egg weight. Body checking had variable relationship with egg number and egg weight. The correlations of shell cracks and body checking with each other and with egg number and egg weight appeared to vary between the strains.