Abstract
The impacts of breeder's strain (Hy-line Brown and Hy-line White 36), flock's age (28, 36, 46, 55 and 66 weeks) and breeding season (summer and winter) on embryonic mortality stages and embryonic malpositions were studied. At each tested age, 120 unhatched eggs from each strain were examined to determine some hatching traits including egg weight, dead embryo (weight and percentage) and shell (weight and percentage). The embryonic mortality phases (early, mid and late) were investigated. The results showed that the embryonic mortality is not uniformly in both genotypes throughout the incubation period. The highest figure of embryonic mortality occurred at the late of hatching stage in the two strains, especially in Brown unhatched eggs. Regarding the malpositions of the embryos, there was a significant difference between layer breeder genotypes for head over right-wing phenomenon; white breeders recorded the highest figure. Likewise, the breeding season had a significant effect on such trait. It could be observed that strain and age of breeders can affect the hatchery performance.