Thus, we hypothesized that particular metabolites in seminal plasma could be considered as markers for sperm freezability. Furthermore, metabolites in seminal plasma may affect downstream and complementary changes in gene/protein expression. A recent study shows that metabolites play a role in sperm energy production, motility, pH control, and regulation of metabolic activity. As metabolites are the final products of metabolism, changes in their composition and content can reflect the state of the sperm and individual metabolic timeliness. Seminal plasma contains a variety of substances, such as proteins, ions, and metabolites including amino acids, lipids, nucleosides, minerals, electrolytes, and steroid hormones. Seminal plasma is composed of secretions from the testis, epididymis, and accessory sex glands. Current knowledge implies that the seminal plasma is much more than a nutrient medium. Sperm freezability is a complex phenotype and it cannot be accurately predicted based solely on conventional parameters. Other freezability markers include patterns of sperm motile subpopulations in extended semen, specific kinetic parameters evaluated at the cooling step, and acrosin activity. In addition, a study demonstrated that genomic differences existed between good and poor freezers in the sequences of polymorphism restriction fragments of 16 candidate genetic markers. Numbers of proteins from sperm or seminal plasma, such as heat-shock protein 90 (HSP90AA1), acrosin-binding protein (ACRBP), triosephosphate isomerase (TPI), and fibronectin 1 (FN1), have been reported as markers for predicting boar ejaculate freezability. Previous research on boar ejaculate freezability biomarkers mainly focused on proteomics. To solve this issue, researchers are engaged in a lot of work to distinguish good (GFE) and poor freezability ejaculates (PFE). Therefore, it is meaningful to distinguish between high and low freezability individuals before cryopreservation procedures and to select high freezability individuals for cryopreservation to improve the efficiency of artificial insemination utilizing post-thawed sperm. On the other hand, the quality of frozen-thawed boar semen shows strong variability in freezability between individuals. On one hand, boar spermatozoa in general presents low freezability because of its high cold shock sensitivity. However, frozen–thawed boar semen accounts for less than 1% of the semen used for insemination. D-aspartic acid, NAG, and inosine in seminal plasma may be potential markers for assessing sperm cryopreservation resistance in boars.Īrtificial insemination has been widely used in pig production worldwide. In conclusion, there is significant difference in the metabolome of seminal plasma between GFE and PFE individuals. Further, twelve metabolites were subjected to metabolic target analysis, and three metabolites (D-aspartic acid, N-acetyl-L-glutamate (NAG), and inosine) showed differences. A total of 953 metabolites were identified in boar semen plasma by UHPLC-qTOF-MS analysis, and 50 metabolites showed significant change between the GFE group and PFE group. Therefore, the main aim of this study was to explore the differences in the metabolic level of seminal plasma between boars with differential freezability and to explore the candidate biomarkers of semen freezability. However, details and significance of the seminal plasma metabolome related to boar sperm freezability are unknown.

The exposure of spermatozoa to small molecules such as metabolites can affect sperm function. The seminal plasma is composed of secretions from the testis, epididymis, and accessory sex glands. Some potential markers of boar sperm freezability have been found in spermatozoa, but little attention has been paid to seminal plasma.

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