| Summary: | In the present study, effects of crossbreeding on egg production traits were evaluated using a 4 × 4 full diallel cross involving four chicken breeds: Improved Horro (H), Sasso (S), Potchefstroom Koekoek (K), and Dz-white feathered (D). The experiment included 800 chickens in a completely randomized design. Data on egg production traits were collected over 40 weeks (WK). Genotypes exhibited significant variations (P < 0.0001) in age at first egg (AFE), body weight at sexual maturity (BWSM), egg weight at first egg (EWAFE), egg number (EN), hen-housed egg production (HHEP), hen-day egg production (HDEP), and egg mass (EM). Heterosis effects (H<sup>e</sup>) varied widely, with positive H<sup>e</sup> for BWSM and EM in most crosses, while AFE consistently showed negative H<sup>e</sup>. All reciprocal crosses showed positive H<sup>e</sup> for EWAFE, while direct crosses had negative values except H × S and H × D. The K × H cross showed the highest H<sup>e</sup> for HHEP (26.85%), HDEP (29.44%), EM (40.88%), and EN (28.27%). The cross D × H also exhibited strong H<sup>e</sup> for HHEP (25.16%) and EN (24.60%), while K × S ranked second for HDEP (22.60%) and EM (33.89%). Reciprocal crosses showed positive H<sup>e</sup> for BWSM, EWAFE, HHEP, HDEP, EM, and EN, except AFE. General combining ability (GCA) and specific combining ability (SCA) effects were highly significant (P<0.0001) for all traits. Reciprocal effects (RE) and maternal effects (M<sup>e</sup>) also influenced trait expression. GCA/SCA ratios indicated that non-additive effects influenced AFE, while additive effects influenced EWAFE. Moderate ratios for HHEP, HDEP, EM, and EN suggested a balance between additive and non-additive effects. Optimizing crossbreeding strategies, aligning with synthetic breed development, using a K sire with H and S dams, and a D sire with H dam, is recommended to improve egg production.
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