Acclimation in Semen Traits and Reaction Time in Large White and Crossbred Boars Exposed to Direct Solar Heat Stress

The objectives of the study were to evaluate and compare acclimation in semen traits of Large White (LW) and Large White x local (LW x LC) F1 (crossbred) boars to high ambient temperatures during exposure to direct solar heat radiation. Twenty-four LW and crossbred boars (12 boars each) were employed for the study. The boars (6 months old, 42.65 – 50.14 kg) were shared into 3 treatments (T) (8 boars/treatment) namely T1 or control (housed), T2 (boars exposed for 45 minutes) and T3 (boars exposed for 60 minutes). Exposure to sun light started each day by 13:30 to 14:15 h (45 min. exposure) and 13:30 to 14:30 h (60 min. exposure) and lasted for 28 days (4 weeks). Data collected and analysed were weekly values of volume of ejaculate (VE), progressive motility (PM), sperm concentration (SC), sperm per ejaculate (SE), percent live sperm (LS), percent abnormal sperm (AS), hydrogen ion concentration (pH), and reaction time (RT). The values of the evaluated parameters were relatively stable and within normal range across the experimental period in boars in the control groups. Volume of ejaculate (VE), PM, SC, SE, and LS decreased progressively and significantly (P?0.05) over the experimental period while AS increased significantly (P?0.05) with experimental period in exposed boars. On the other hand RT increased initially but became stable from wk 2 of exposure. The degeneration in semen quality in exposed boars was generally more rapid in LW compared to crossbred boars. Also RT was shorter for crossbred boars compared to LW boars. It was concluded that LW and crossbred boars exposed to direct solar radiation were unable to acclimate and restore normal or stable semen parameters for the duration of the study whereas acclimation occurred in RT after 2 weeks of exposure. Furthermore, considering the values for semen traits, the crossbred boars were more resistant to heat stress than their LW counterparts.