Inter-male variability in sperm cryotolerance of Saanen bucks assessed using a purpose-built Sperm Quality Index

Sperm cryopreservation is an essential tool for animal breeding and genetic conservation programs. However, the freeze–thaw process induces structural and functional alterations that compromise sperm survival and fertilizing ability. Although inter–individual variability in sperm cryotolerance has been widely reported in livestock species, integrative approaches for evaluating semen freezability in goats remain limited. Therefore, the present study evaluated sperm cryotolerance in Saanen bucks using composite Sperm Quality Indexes (SQI) derived from multiple post-thaw sperm functional parameters. A total of 124 ejaculates from seven adult Saanen bucks were cryopreserved and evaluated after thawing for progressive motility, viability, acrosome integrity, capacitation status, and plasma membrane fluidity. Two indices were calculated: SQI1, which includes parameters associated with sperm functionality preservation, and SQI2, which includes indicators of cryo-induced cellular damage. Significant inter–male differences were observed for both indices (P < 0.05). Male 1 exhibited lower SQI1 values and higher SQI2 values than males 6 and 7, indicating reduced sperm cryotolerance and increased susceptibility to cryo–induced membrane destabilization and capacitation–like changes. The remaining males showed intermediate responses without significant differences among them. The proposed SQIs successfully detected biologically meaningful inter-male differences in sperm cryotolerance and constitute a useful approach for identifying bucks with different freezing responses.