Equex-STM Paste-Added Freezing Medium and Straw Volume Influence Hampshire Crossbred Boar Semen Quality Following Cryopreservation

Abstract

Cryopreservation of boar semen is essential for maintaining genetic diversity and improving reproductive efficiency. However, optimizing semen extenders and packaging methods is crucial to enhancing sperm quality and cryotolerance. Equex-STM is commonly used as a surfactant to enhance cryoprotective properties by stabilizing sperm membranes during freezing and thawing. A total of 24 ejaculates (n = 24), six from each of four Hampshire crossbred boars, aged between 18 and 24 months were used in the present study. Semen was collected twice weekly by gloved hand technique. The sperm-rich fraction showing more than 70% initial motility was considered for further processing and freezing. The fresh semen was diluted in Beltsville thawing solution (BTS) at a 1:1 ratio and further processed with the addition of Fraction I and Fraction II extenders supplemented with and without 1.5% Equex-STM paste {Control (C)-no Equex; Treatment (T—1.5% Equex-STM supplementation}. The extended semen was packaged in 0.25 and 0.5 mL straws to check the effect of straw size (T₁—0.25 mL straw and T₂—0.50 mL straw). Straws were cryopreserved in liquid nitrogen (LN₂) for post-thaw sperm quality evaluation. Results showed that the sperm motility, viability, plasma membrane integrity (PMI), DNA integrity, and mitochondrial membrane potential (MMP) were significantly (p < 0.001) higher in the T group in comparison with control (C). Sperm motility, PMI, and DNA integrity were highly significant (p < 0.001) and sperm viability and MMP were significant (p < 0.05) in group T₂ in comparison with T₁.

In conclusion, supplementation of 1.5% Equex-STM in the freezing medium and packaging in 0.5 mL straw have better cryotolerance of frozen Hampshire crossbred boar semen in comparison with 0.25 mL straw.