Animal Molecular Breeding 2024, Vol.14, No.3, 239-251 http://animalscipublisher.com/index.php/amb 245 5.3 Outcomes and benefits The outcomes of implementing GS in dairy cattle have been profound. The most significant benefit has been the acceleration of genetic gain. For example, since the adoption of GS, the rate of genetic improvement for traits such as milk yield, fat, and protein content has nearly doubled in some breeds. The reduction in generation intervals-rom over five years to less than three years for bull selection-has also contributed to this increased rate of genetic gain (Guinan et al., 2022). Moreover, GS has led to cost savings by reducing the need for extensive progeny testing, which was previously a major expense for breeders. The technology has also allowed for more targeted selection, improving the overall health, fertility, and productivity of dairy herds. The ability to screen for and manage inbreeding through genomic data has been another key benefit, helping to maintain genetic diversity while optimizing breeding outcomes (Gutierrez-Reinoso et al., 2021). 5.4 Challenges and lessons learned Despite the many benefits, the implementation of GS in dairy cattle breeding has not been without challenges. One of the primary issues has been the potential for increased inbreeding, as the use of a limited number of top sires can lead to a reduction in genetic diversity over time. This has raised concerns about the long-term sustainability of breeding programs, particularly in small or isolated populations (Obari et al., 2022). Additionally, the high costs associated with genotyping, especially in the early stages of GS adoption, have been a barrier for smaller breeding operations. However, as the cost of genotyping continues to decrease, more breeders are expected to adopt GS. Another challenge has been the need for ongoing education and support for breeders to fully understand and utilize GS technologies effectively. Lessons learned from the U.S. experience highlight the importance of developing robust reference populations, investing in infrastructure for data collection and analysis, and ensuring that breeders have access to the necessary tools and knowledge to implement GS successfully (Figure 2) (Wiggans et al., 2017). Figure 2 Number of genotyped animals included in US genomic evaluations for dairy cattle since January 2009 (Adopted from Wiggans et al., 2017) Note: Official US genomic evaluations were first released to the dairy industry in January 2009 for Holsteins and Jerseys, in August 2009 for Brown Swiss, in April 2013 for Ayrshires, and in April 2016 for Guernseys. Data for figure generation were reported by the Council on Dairy Cattle Breeding (27). Months without data represent months in which official evaluations were not released. (Adapted from Wiggans et al., 2017) 6 Challenges and Limitations of Genomic Selection Despite its transformative potential, the application of genomic selection (GS) in livestock breeding is not without challenges and limitations. These range from ethical considerations to economic barriers, concerns about genetic diversity, and technical and practical challenges. Addressing these issues is essential for the sustainable and equitable use of GS in the livestock industry.
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