Effect of sex-sorting on the ability of fresh and cryopreserved bull sperm to undergo an acrosome reaction

Previous studies indicate that sex-sorted sperm exhibit different physiology, including fertilizing capacity, from non-sorted sperm. However, differences between X- and Y-bearing sperm in their ability to undergo an acrosome reaction have never been investigated. This study determined the ability of non-sorted and sex-sorted sperm to undergo the acrosome reaction prior to and after cryopreservation. Sperm were treated with dilauroylphosphatidylcholine (PC12) to induce the acrosome reaction and the percentages of live-acrosome-reacted sperm and dead sperm were evaluated. The X- and Y-bearing sperm reacted similarly to the PC12 treatment, regardless of whether sperm were assessed prior to or after cryopreservation. Fresh control sperm exhibited lower percentages of live sperm (60%) than either X- or Y- sorted sperm (69-74%, P < 0.05). Percentages of live control sperm were also lower after thawing (29-35%) than sex-sorted sperm (55-58%, P < 0.05). Control and sex-sorted fresh sperm responded similarly to PC12 treatment. However, sex-sorted cryopreserved sperm exhibited higher percentages of live-acrosome-reacted sperm (23%) than control sperm (9%, P < 0.05) after 40 min without PC12 treatment. In addition, cryopreserved control sperm treated with 79 μM PC12 exhibited higher percentages of live-acrosome-reacted sperm than sex-sorted sperm. In conclusion, X- and Y-bearing sperm responded similarly to PC12 treatment. In addition, fresh sexed and non-sorted sperm responded similarly to PC12 treatment. However, cryopreserved sex-sorted sperm underwent an acrosome reaction more rapidly in the absence of PC12 (over a 40 min period) than the non-sorted sperm. Therefore, sex-sorting induced changes in sperm membranes that accelerated the acrosome reaction process in sperm after cryopreservation.