International Journal of Molecular Zoology 2024, Vol.14, No.5, 265-272 http://animalscipublisher.com/index.php/ijmz 268 Figure 2 Use of assisted reproductive technologies to generate the next generation of elite dairy, elite dairy-beef, and commercial beef calves. (A) To create the next generation of dairy AI bulls and dairy bull dams, embryos are generated from elite dairy dams by superovulation and AI or by using ovum pick-up (OPU) or laparoscopic OPU (LOPU) or juvenile in vitro fertilization and embryo transfer (JIVET) to collect oocytes followed by in vitro maturation (IVM), fertilization (IVF) with semen from elite dairy bulls, and culture (IVC) to produce embryos for transfer (ET) to recipient dairy dams not required to generate replacement females (either surplus to requirements or genetically inferior). (B) To create the next generation of dairy-beef AI bulls and dairy-beef bull dams, superovulation and AI or OPU and LOPU followed by IVF with semen from elite dairy-beef bulls (e.g., Angus) is conducted on elite dairy-beef dams to generate embryos for transfer to recipient dairy dams. (C) To produce commercial beef animals, ovaries collected postslaughter from beef-cross heifers are used as a source of low-cost oocytes. These oocytes are fertilized with semen from elite dairy-beef bulls (different breed to maximize heterosis), resulting in embryos suitable for transfer to recipient dairy dams. The male and female offspring are all commercial beef animals, with female offspring also being a potential source of oocytes after slaughter (Adopted from Crowe et al., 2021) 4.3 Case studies demonstrating genomic selection effects Several case studies highlight the effectiveness of GS in improving fertility traits in beef cattle. For example, a study on composite gene combination (CGC) beef cattle demonstrated that genomic prediction accuracy was higher for AOP compared to AOC, likely due to the higher heritability of AOP. Another study on Charolais and Limousin beef cows identified significant single nucleotide polymorphisms (SNPs) associated with reproductive and productive traits, suggesting the potential for incorporating these genetic markers into breeding programs (Keogh et al., 2020). Additionally, research on Retinta beef cattle revealed high heritability estimates for
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