Genetic analysis of egg production traits in four chicken breeds using a full diallel cross

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^e) varied widely, with positive H^e for BWSM and EM in most crosses, while AFE consistently showed negative H^e. All reciprocal crosses showed positive H^e for EWAFE, while direct crosses had negative values except H × S and H × D. The K × H cross showed the highest H^e for HHEP (26.85 %), HDEP (29.44 %), EM (40.88 %), and EN (28.27 %). The cross D × H also exhibited strong H^e 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^e 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^e) 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.