Effect of season, genetic line and temperature during transport on sperm motility of commercial insemination doses of pooled boar semen: A retrospective study

Commercial pooled semen from boars of maternal and terminal genetic lines was analysed over two consecutive years, as part of an external quality control program. Semen doses were prepared for two total sperm counts (2.0 × 10⁹ /75 ml [n = 578] and 1.5 × 10⁹ /34 ml [n = 643]). Semen doses were evaluated for motility, morphology and bacterial contamination at days 1 and 4 after collection. Additionally, temperature during transport was tracked and correlated to sperm motility. Sperm motility and morphology were significantly affected by genetic line, but not by total sperm per doses. Total motility (TM) was affected (p < .05) by season. Progressive motility (PM) was lower (p < .05) in some winter months, and higher (p < .05) in summer for maternal-line doses. Normal sperm morphology was higher (p < .05) in some months of late fall and winter, with an apparent decrease in some summer months. In general, motility was significantly higher on day 1 than on day 4, and was also affected (p < .05) by temperature, especially for terminal-line doses. Semen doses exposed to >15°C had higher (p < .05) TM, VSL (straight-line velocity) and linearity than doses exposed to <15°C. Progressive motility and straightness increased (p < .05) proportionally with temperature. At day 1, motility, average path velocity (VAP) and VSL increased (p < .05) with temperature, and was higher than the corresponding group at day 4, except for VSL. Sperm motility and kinematics at day 4 were similar between temperature groups, except for doses exposed to >20°C that had higher (p < .05) VAP and VSL than doses exposed to <12°C. Microbiology evaluation revealed that less than 8.2% (15/184) of the semen doses had bacterial growth. Sphingobacterium lactis was the most prevalent bacterium identified. In conclusion, genetic line strongly influences sperm motility, while total sperm count does not have an impact. Transient reduced temperatures during shipping do not impair sperm quality after 4 days of storage. Seasonal and temperature effects on sperm motility of pooled boar semen are not overcome by pre-production ejaculate selection and semen pooling.