Comparative Analysis of Classic Semen Extenders for Frozen-Thawed Boar Semen

The physiological functions of mammalian sperm, such as motility, hyperactivation, and capacitation, require substantial energy. This study investigates the effects of two classic cryopreservation extenders-TCG (tris-citrate-glucose) and LEY (lactose-egg yolk)-on the energy metabolism of frozen-thawed boar semen. By comparing the quality indicators, key metabolite levels, and the activities of critical enzymes involved in glycolysis and the tricarboxylic acid cycle, we aim to understand how these different semen extenders influence the spermatozoa vitality of frozen-thawed boar semen. Following thawing, the LEY-cryopreserved sperm demonstrated significantly elevated motility parameters (viability, VCL, VSL, and VAP) and enhanced plasma membrane and acrosomal integrity compared with the TCG group (p < 0.05), though both cryopreserved groups exhibited significantly reduced performance relative to fresh semen controls. Cryopreservation markedly reduced intracellular adenosine triphosphate (ATP), pyruvate, and acetyl coenzyme A (A-CoA) levels (fresh > LEY > TCG; p < 0.05). The LEY-preserved spermatozoa retained higher activities of glycolysis-related enzymes (phosphofructokinase, PFK; pyruvate kinase, PK) compared with the TCG group, which, in turn, showed elevated lactate dehydrogenase (LDH) activity. Critically, TCG-suppressed pyruvate dehydrogenase (PDH) activity (p < 0.05) coincided with diminished A-CoA, indicating impaired mitochondrial oxidative phosphorylation. These results demonstrate LEY's superior preservation of motility and membrane stability but highlight cryodamage-induced energy metabolism dysregulation, particularly TCG's disruption of the glycolysis-TCA cycle coordination essential for spermatozoa function. In conclusion, the choice of semen extender has a significant impact on the energy metabolism and overall quality of frozen-thawed semen, highlighting the importance of optimizing cryopreservation protocols for improved spermatozoa viability and functionality.