Genetic study of embryonic mortality in White Leghorn lines selected for egg production traits

The present study compares embryonic mortality between lines selected for different production traits, assesses the effects of inbreeding of the hen and embryo on embryonic mortality, and estimates genetic parameters of embryonic mortality. The experiment covered 10 generations of selection for increased egg number (EN), egg weight (EW), egg mass (EM) and a control line (C). The data included age at 1st egg, egg number and egg weight. Percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent dead chick at hatch (PDH) were also recorded for the selected parents. PDH was higher in the selected lines than in the control line. Among the selected lines, the EW line had the highest embryonic mortality. Inbreeding of the hen and embryo had no significant effect on PDH in any of the lines. Estimates of heritability for PDH were 0.10+/-0.05, 0.02+/-0.02, 0.03+/-0.02 and 0.02+/-0.02 for lines EN, EW, EM and C, respectively. There was a positive genetic correlation between egg weight and PDH in line EW indicating that selection for increased egg weight was associated with high embryonic mortality. A negative genetic correlation between PDH and reproductive traits in line EN was observed, which is favourable.