International Journal of Molecular Zoology 2024, Vol.14, No.5, 265-272 http://animalscipublisher.com/index.php/ijmz 267 In dairy cattle, the implementation of GS has led to significant improvements in traits of economic importance, such as milk production, fertility, and longevity. The rate of genetic gain has doubled, and the costs associated with progeny testing have been reduced (Guinan et al., 2022). In beef cattle, although the adoption of GS has been slower due to different breeding structures, studies have shown that selective genotyping can improve prediction accuracy even with a limited number of genotyped animals (Mohammaddiyeh et al., 2023). 3 Fertility Traits in Beef Cattle 3.1 Key fertility traits affecting beef production Key fertility traits that significantly impact beef production include age at first calving (AFC), calving interval (CI), and heifer pregnancy status (HPS). Age at first calving is crucial as it determines the onset of a cow's reproductive life and influences lifetime productivity. Calving interval, the period between successive calvings, affects the number of calves a cow can produce over her lifetime. Heifer pregnancy status, which indicates whether a heifer becomes pregnant during the breeding season, is essential for ensuring that heifers contribute to the herd's productivity (Toghiani et al., 2017; Brzáková et al., 2020). 3.2 Genetic basis of fertility traits The genetic basis of fertility traits in beef cattle is complex and involves multiple genes. Heritability estimates for these traits are generally low to moderate, indicating that while genetic selection can improve these traits, environmental factors also play a significant role. For instance, heritability for age at first calving ranges from 0.03 to 0.31, and for calving interval, it is similarly low (Berry and Evans, 2014). Genomic selection has shown promise in improving the accuracy of predicting these traits, with studies identifying specific single nucleotide polymorphisms (SNPs) associated with reproductive efficiency (Melo et al., 2018; Keogh et al., 2020; Jiménez et al., 2023). However, the genetic correlations between fertility traits and other performance traits, such as growth and carcass traits, can be antagonistic, complicating selection strategies (Pardo et al., 2020). 3.3 Challenges in measuring fertility traits Measuring fertility traits in beef cattle presents several challenges. One major issue is the low heritability of these traits, which makes genetic improvement slow and difficult. Additionally, the collection of accurate phenotypic data is labor-intensive and time-consuming, often requiring long-term monitoring of individual animals (Zhang et al., 2014). Environmental factors, such as nutrition, management practices, and climate, also significantly influence fertility traits, adding variability that can obscure genetic effects. Furthermore, the complexity of reproductive physiology means that multiple traits must be considered simultaneously, complicating the analysis and interpretation of data (Berry et al., 2014; Meier et al., 2021). 4 Impact of Genomic Selection on Fertility Traits 4.1 Genetic gain in fertility traits through genomic selection Genomic selection (GS) has shown significant potential in enhancing genetic gain for fertility traits in beef cattle. Studies have demonstrated that GS can improve the predictive accuracy and genetic gain of various fertility traits, such as age of puberty (AOP), age at first calving (AOC), and heifer pregnancy status (HPS). The heritability estimates for these traits were found to be higher when using genomic approaches compared to traditional pedigree-based methods, indicating a more effective selection process (Toghiani et al., 2017). Additionally, the introduction of GS in dairy cattle has led to increased genetic trends for fertility, lifespan, and udder health, suggesting similar potential benefits for beef cattle (Figure 2) (García-Ruiz et al., 2016). 4.2 Impacts on reproductive efficiency and profitability The implementation of GS has positively impacted reproductive efficiency and profitability in beef cattle production. Improved reproductive efficiency, particularly in traits with low heritability, can lead to significant economic benefits (Berry et al., 2014). For instance, the use of GS has been associated with increased rates of genetic gain and inbreeding in the Australian national herd, which has implications for long-term productivity and profitability (Scott et al., 2021). Furthermore, advancements in genomic technologies have enabled more accurate selection for reproductive traits, thereby enhancing overall herd fertility and reducing economic losses associated with subfertility (Thundathil et al., 2016; Fonseca et al., 2020).
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