Genetic analysis of egg-shell abnormalities in layer chickens

Egg-shell abnormalities, viz. pimpling, windows and body checking and other abnormalities were assessed on 52 125 eggs collected form 2 171 pullets of 2 selected White Leghorn strains, (PL1 and PL2) between 36 and 40 weeks of age. Strain PL 2 as compared to strain PL 1 had higher incidence of pimple d eggs (4.1 vs 1.6%) but lower incidence of window (1.2 vs 1.4%) and body-c hecked(3.1 vs 4.2%) eggs. The sire-component heritabilities varied between 0.03+/-0.05 and 0.33+/-0.13 for pimpling;between 0.05+/-0.04 and 0.09+/-0.0 5 for windows; between 0.13+/-0.06 and 0.18+/-0.08 for body checking, and 0 .06+/-0.05 and 0.21+/-0.09 for total shell abnormalities. Dam-component est imates were higher for pimpling but Lower for other shell traits than the s ire component estimates. Total shell abnormalities had high genetic and phe notypic correlations with pimpling and body checking. The genetic correlati ons of body checking with pimpling and windows were extremely low but pimpl ing had moderate to high negative genetic correlation with windows. Most of the economic traits also did not bear strong and consistent genetic correl ations with shell-abnormalities. However, the genetic correlation was consi stent in the 2 strains between egg weight and body checking (0.24+/-0.17 an d 0.62+/-0.13) and between egg number and pimpling (0.13+/-0.19 and 0.34+/- 0.26).