Genomic Regions and Candidate Genes Associated With Semen Traits in Rams: A Systematic GWAS Review With Implications for South African Sheep Breeds

Ram fertility is a key determinant of reproductive efficiency in sheep production systems, particularly under extensive and semi-extensive conditions prevalent in South Africa. Semen quality traits, including ejaculate volume, sperm concentration, motility, and cryotolerance, exhibit measurable genetic variation and are increasingly investigated using genomic approaches. This systematic review synthesizes evidence from three eligible Genome-Wide Association Studies (GWAS) analyses that have identified genomic regions and candidate genes associated with semen traits in rams. Across Merino, Assaf, and composite populations, semen traits were consistently shown to be polygenic, involving genes linked to spermatogenesis, energy metabolism, oxidative stress regulation, and membrane integrity. Comparative analysis revealed both shared and breed-specific genomic regions, reflecting differences in genetic architecture and selection history. However, no studies were conducted in South African sheep populations, limiting the direct applicability of these findings. Comparative analysis revealed both shared and breed-specific genomic regions, highlighting variation in genetic architecture across populations. However, the absence of studies conducted in South African sheep breeds limits the direct applicability of these findings and underscores the need for locally relevant genomic research.