Animal Molecular Breeding 2024, Vol.14, No.1, 62-71 http://animalscipublisher.com/index.php/amb 68 Another example is the progress in layer breeding. Gao et al. (2022) discovered several genetic loci that affect eggshell strength and egg size through GWAS analysis. These findings were used to guide selective breeding, resulting in laying hen breeds that were both highly productive and capable of producing high-quality eggs. This not only increases the market value of eggs, but also reduces losses during the production process and significantly improves breeding efficiency. 5.2 Application of GWAS in disease resistance research Disease is a major challenge in poultry production, and genetic improvement offers an effective way to increase poultry's resistance to disease. Genome-wide association studies (GWAS) are particularly useful in this area, helping scientists identify genetic variants associated with disease resistance. Take avian influenza, for example, a disease that has had a huge impact on the poultry industry. Through GWAS analysis, Drobik-Czwarno et al. (2019) discovered some genetic markers related to avian influenza resistance. These findings were then used in breeding programs with the goal of creating chicken breeds with higher resistance to avian influenza. The application of this method significantly reduces the threat of avian influenza to the chicken industry, while reducing reliance on vaccines and drugs. Also, there is research on Marek's disease (a viral disease of chickens) (Figure 3). GWAS not only help scientists identify genetic variants associated with disease resistance, but also reveal the complexity of disease resistance mechanisms. These studies provide valuable information for the development of new disease control strategies and guide the implementation of disease-resistant breeding programs. Figure 3 Circos plot illustrating CNV regions in nine chicken lines (Bai et al., 2020) Note: Regions with copy number events are plotted within the nine light yellow inner tracks; Copy number changes indicated by two different statuses (deletion or duplication) are shown in the inner circle plot using the RCircos; Plot function in RCircos package; The outermost circle displays the chicken chromosomes (chrZ and chrW were excluded); The circles from outside to inside represent Lines 72, 63, F1, RCS-A, M, J, D, L and X 5.3 Future breeding plans As climate change and environmental pressures increase, future poultry breeding programs will focus more on improving adaptability and sustainability. Towards this goal, scientists are exploring the use of advanced technologies such as GWAS to discover genetic resources that can help poultry adapt to extreme environmental conditions. One future breeding direction is to improve heat stress tolerance in poultry. As global temperatures rise, the impact of high temperatures on poultry is becoming increasingly severe, so it is particularly important to breed chickens
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