Cryopreservation of bull semen shipped overnight and its effect on post-thaw sperm motility, plasma membrane integrity, mitochondrial membrane potential and normal acrosomes

In the Canadian Animal Genetic Resource Program, bull semen is donated in frozen or fresh (diluted) states. This study was designed to assess the cryopreservation of diluted bull semen shipped at 4 °C overnight, and to determine the post-thaw quality of shipped semen using different straw volumes and freezing rates. Semen was collected from four breeding bulls (three ejaculates per bull). Semen was diluted in Tris–citric acid–egg yolk–glycerol (TEYG) extender, cooled to 4 °C and frozen as per routine (control semen). After cooling to 4 °C, a part of semen was removed and shipped overnight to the research laboratory via express courier (shipped semen). Semen was packaged in 0.25 or 0.5 ml straws and frozen in a programmable freezer using three freezing rates, i.e., −10, −25 or −40 °C/min. Control semen was also shipped to the research laboratory. Post-thaw sperm motility characteristics were assessed using CASA, and post-thaw sperm plasma membrane, mitochondrial membrane potential and normal acrosomes were assessed using flow cytometry. Post-thaw sperm quality was greater in shipped semen as compared to control (P < 0.001). The shipped semen packaged in 0.25 ml straws had better post-thaw sperm quality than in 0.5 ml straws (P < 0.001). Freezing rate had no effect on post-thaw sperm quality. In conclusion, bull semen can be shipped overnight for subsequent cryopreservation and gene banking. Overnight shipping of semen was found advantageous for bull semen cryopreservation. Semen packaging in 0.25 ml straws yielded better post-thaw quality than 0.5 ml straws.