International Journal of Molecular Zoology, 2025, Vol.15, No.2, 90-100 http://animalscipublisher.com/index.php/ijmz 94 4 Research and Practice on the Enhancement of Growth Performance through Hybridization 4.1 Breeding examples of fast-sized broilers The breeding of modern fast-sized broilers fully demonstrates the successful practice of hybridization strategies in improving growth performance. From the mid-20th century to the present, through continuous crossbreeding and selection, the growth rate of broilers has significantly increased: the number of days required for broilers from breeding to market has been reduced by more than half, while their body weight has increased several times (Gilyazova et al., 2025). The current mainstream commercial broiler breeds (such as Ross 308, Cobb 500, etc.) are all bred from four-line or three-line hybrid lines. Research shows that the F1 hybrid generation of broilers can increase the hybridization advantage in growth rate by approximately 10%-20% compared to the average of their parents. For instance, when the fast-growing but low-egg-laying White Rock rooster was crossed with the high-egg-laying Conish hen, the average body weight of the offspring at 42 days was approximately 15% higher than that of the parents, significantly higher than that of any parent breed (Wang et al., 2022). For instance, the father of the "Short-legged yellow Chicken" bred by Hebei Agricultural University was crossed with the mother of the green-shelled laying chicken from Shandong. In the F1 generation, not only was the high-quality meat quality maintained, but the growth rate was also increased by more than 30% compared to the mother. In addition, hybrid broilers also performed well in pectoral muscle rate (proportion of pectoral muscle to carcass) and carcass quality, which was related to the contribution of strong muscle growth genes in paternal breeds (Yang et al., 2021; Dadfar et al., 2023). 4.2 Hybridization strategy of local varieties × high-quality father parents Crossbreeding local chicken breeds with improved ones is an effective way to enhance the production performance of local chickens. Local breeds (such as free-range chickens from various regions) usually have strong adaptability and good meat flavor, but their growth and meat production performance are not as good as those of improved breeds. By crossbreeding with high-quality paternal breeds, it is possible to significantly increase the weight gain rate and feed utilization rate while maintaining the characteristics of local chickens. For instance, the "Sanhuang Chicken" from Jiangxi Province is renowned for its delicious meat, but it gains weight relatively slowly. White-feathered broilers were introduced as the sire and crossbred with them. The weight of the offspring at 70 days of age was 20% higher than that of pure Sanhuang chickens, and the meat quality score remained close to that of free-range chickens. For example, when the Yao chicken in Guangxi was crossed with the fast-growing chicken breed, the growth period of the offspring was shortened by about 30 days, and the flavor and stress resistance of the mother were basically retained (Fu et al., 2023). It should be noted that local varieties have rich genetic diversity and significant individual differences, and the hybridization effect varies depending on the quality of the mother. Therefore, before implementing hybridization improvement, it is often necessary to conduct phenotypic and genetic evaluations of local populations, and select those with better production performance as the mother to ensure that the performance of the hybrid offspring is significantly enhanced. Meanwhile, excessive reliance on single hybridization to introduce foreign blood should be avoided. Stepwise hybridization or rotational hybridization should be carried out as needed to gradually stabilize the new strain (Ramteke et al., 2025). 4.3 Application of molecular marker-assisted and genomic selection in hybridization Traditional hybrid breeding mainly relies on phenotypic determination and statistical evaluation. The rise of molecular breeding technology has injected new vitality into hybrid breeding. Among them, molecular marker-assisted selection (MAS) and genomic selection (GS) have been applied in domestic chicken breeding and can be used to optimize hybrid parents and predict the performance of hybrid offspring (Xiong et al., 2024). A study showed that when hormone receptor gene markers were applied for selection (such as FSHR and PRLR genotypes) in an laying hen line, the egg production of the first-generation hybrid was 3% higher than that of the control without MAS (Kulikov et al., 2023).
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