Effect of Pre-Freezing 18 °C Holding Time on Post-Thaw Motility and Morphometry of Cryopreserved Boar Epididymal Sperm

The study investigated the sperm motility and morphometry of pre-freeze and post-thaw boar epididymal semen cooled at increasing holding times at 18 °C. A total of 50 testes of heterogeneous boars were collected (5 testes/day) from the local abattoir and transported to the laboratory at 5 °C within 30 min after slaughter. Semen was retrieved from the caudal part of the epididymis using the slicing float-up method, diluted with Beltsville Thawing Solution extender, pooled in a 50 mL centrifuge tube/5 testes/day, and cooled at 18 °C. Following each holding time (0, 3, 6, 9, 12, 24, and 48 h), the cooled semen sample was re-suspended with Fraction A extender and stored at 5 °C for an additional 45 min. A cooled resuspended semen sample was then diluted with Fraction B extender, loaded into 0.25 mL straws, and frozen using liquid nitrogen vapour. Thawing was accomplished by immersing the semen straws in warm (37 °C) water for 1 min and the samples were evaluated for sperm motility and morphometry traits using the computer-assisted sperm analyzer system. The data were analyzed using variance analysis. Descriptive statistics were used to assess sperm morphometry, establishing the minimum and maximum values. Boar epididymal sperm survived for up to 48 h when held at 18 °C. Furthermore, the highest post-thawed sperm motility rates were observed in semen frozen after 3 h of holding time, with a sperm total motility of 85.9%, a progressive motility of 60.3%, and a rapid motility of 33.2%, as compared to other holding times (<i>p</i> < 0.05). The acceptable ranges for pre-freeze and post-thawed sperm morphology were head length (8.4–9.1 µm), width (4.4–4.8 µm), area (29.9–38.2 µm²), perimeter (20.1–23.7 µm), midpiece width (1.1–2.8 µm), and sperm shape, were consistent regardless of the holding time. A holding time of 3 h enhances the cryoresistance of sperm cooled at 18 °C. Therefore, these findings suggest that boar epididymal sperm can be effectively conserved and can maintain fertilization capability when cooled for 3 h at 18 °C before freezing.