Effect of dilution temperature on boar semen quality

As boar semen is very sensitive to cold shock and changes in temperature during semen processing can have a profound impact on semen quality, the effect of the extender temperature at the time of dilution was investigated in a two-step dilution protocol for boar semen being processed for liquid storage. Fifteen boars of different breeds and ages from a commercial artificial insemination centre were included. One ejaculate per boar was collected and processed with Beltsville Thawing Solution semen extender. Each ejaculate was diluted (1 : 1) at 30 °C, and subsequently, the samples were diluted (30 × 10(6) sperm/ml) with either preheated extender [29.3 °C ± 0.2 °C, group A (GA)] or extender at room temperature [22.7 °C ± 0.6 °C, group B (GB)]. Samples were transported to the Faculty of Veterinary Medicine (University of Ghent, Belgium) in two isotherm boxes (one per group), stored at 17 °C and investigated for three consecutive days (D0 to D2). At D0, D1 and D2, motility parameters [computer-assisted semen analysis (CASA)] and the per cent of sperm with intact membrane (% IM) by eosin nigrosin staining were evaluated. At D0 and D2, the % of sperm with intact acrosome (% IA) was studied by Pisum sativum agglutinin staining. The average temperature of the 1 : 1 dilution was 29.4 °C ± 1.1 °C immediately after extender addition. No significant differences were found between groups for per cent motility [79.3 ± 9.0 for GA and 81.1 ± 9.2 for GB (p = 0.372)], % progressive motility [56.5 ± 13.3 for GA and 58.4 ± 13.8 for GB (p = 0.737)] or any CASA parameter. No differences were found for % IM [85.1 ± 10.7 and 84.5 ± 3.8 for GA and GB, respectively (p = 0.761)] and % IA [72.2 ± 9.4 for GA and 68.3 ± 16.6 for GB (p = 0.792)]. In conclusion, when a two-step dilution is performed, preheating the extender for the second dilution to match the semen temperature did not result in better semen quality compared to a dilution at a moderate room temperature.