Variance and covariance component analysis of incubational mortality in chickens

A total of 1,33,507 eggs obtained from 7864 pullets of two selected White L eghorn strains over four generations representing 304 sires and 1669 darns were incubated. The unhatched eggs were broken-open for examination of embr yonic development and classified as early-dead (0-11d), late-dead (12-22d) and pips. The sire component heritabilities (%) pooled over years in the tw o strains, respectively were 10.5+/-3.4 and 11.0+/-3.2 for total incubation mortality; 2.2+/-2.2 and 5.1+/-2.4 for early-dead; 6.8+/-3.0 and 8.0+/-3.0 for late-dead and 8.7+/-3.1 and 4.8+/-2.4 for pips. Total embryonic mortal ity as well as its three components had high genetic correlations amongst e ach other. However, the genetic correlations of pipping mortality with earl y and late mortality were weaker as compared with those of early and late m ortality.