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 Leghorn strains over four generations representing 304 sires and 1669 darns were incubated. The unhatched eggs were broken-open for examination of embryonic development and classified as early-dead (0-11d), late-dead (12-22d) and pips. The sire component heritabilities (%) pooled over years in the two 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 mortality as well as its three components had high genetic correlations amongst each other. However, the genetic correlations of pipping mortality with early and late mortality were weaker as compared with those of early and late mortality.