Effect of crossing on the performance of local chicken strains. 4 - effect of strain and laying age on egg quality characteristics.

An experiment was conducted to evaluate the effect of Gimmizah (G), and Bandara (B) chicken strains and their crosses (G x B) and (B x G) on egg quality characteristics throughout two laying age periods (38-42) and (62-66) weeks. Chickens of each genotype were kept in family pens and randomly divided into 5 replicates (12 layer hens per pen). External and internal egg quality parameters were determined for both strains and their crosses at each laying age period. The phenotypic correlations between external and internal egg quality characteristics were detected. Also, hybrid vigor between crosses for egg quality characteristics was detected at two age periods. Gimmizah chickens strain significantly (p<0.01) produced heavier egg weight compared to those produced from B ones and crosses. Egg weight was significantly (p<0.01) increased with advancing layer age among all experimented genotypes. Eggshell weight was significantly heavier in eggs produced from G strain and its crosses (G x B) and (B x G) compared to those produced from B strain which recorded the lowest one. The highest numerical eggshell percentage was produced from G strain and its cross at early age period but this observation is not true in the later laying period. Age had a significant effect on eggshell thickness as it decreased with hen age. Bandara chicken strain recorded the lowest significant (p<0.01) yolk weight compared with those for crossing with G x B. The yolk weight was not affected by layers age in all experimented genotypes. The yolk percentage in G x B cross was significantly (p<0.01) superior to those for G and B strains. Haugh units were not significantly different between experimented pure strains and their crosses, but hen age significantly (p<0.01) affected this trait. Moreover, hen age had a