Biomarkers of sperm fertility in pigs: a relevant tool for the discrimination of sub‑fertile males?

In internally fertilizing animals, such as the pig, males transfer not only spermatozoa but also a complex mixture collectively termed seminal plasma (SP). SP contains diverse bioactive components, including proteins, peptides, cytokines, and various RNA species. Growing evidence indicates that SP contributes not only to the sperm quality but also modulates the female's immune responses. Major progress in biological knowledge and in the discovery of sperm quality biomarkers has been driven by advances in biotechnology and by the increasing affordability of omics technologies. With modern proteomic, (epi)genomic, transcriptomic, metabolomic, and functional analyses applied directly to semen, it is now possible to evaluate not only the functional state of the testes, epididymis, and accessory glands, but also to predict fertility through emerging biomarkers. Beyond diagnostics and fertility forecasting, new opportunities arise from the sperm quality biomarker definition using semen additives-such as specific molecules (proteins, peptides, enzymes) or extracellular vesicles (EVs). These EVs contain bioactive cargo protected within nanovesicles that can be isolated, stored, or even produced de novo in vitro. Boar spermatozoa are notoriously difficult to cryopreserve because they lose cholesterol during handling. EVs could fuse with sperm cells, deliver cholesterol‑rich lipids to the sperm membrane, and transfer specific proteins and nucleic acids. This raises the possibility that harvesting EVs, especially from highly fertile males, could be used in the future to improve sperm storage and even cryopreservation. Taken together, this review aims to list sperm fertility biomarkers that could be useful for the AI companies to discriminate sub-fertile males at an early stage.