Sex-sorted bovine spermatozoa and DNA damage: II. Dynamic features.

This study examined the dynamic response of Spermatozoa DNA Fragmentation after sex selection in bulls using a MoFlo(®) SX (Beckman Coulter, Miami FL) spermatozoa sorter. The dynamic response of spermatozoa DNA fragmentation refers to the changing values of SDF, i.e., rate of SDF (rSDF), when analyzed periodically over a set incubation time at 37 °C. A dynamic assessment of SDF using non-sorted and sex-sorted spermatozoa samples during 72 h of incubation at 37 °C was performed. Results showed a reduced DNA longevity in sex-sorted frozen-thawed spermatozoa, with spermatozoa DNA damage appearing between 24 h and 48 h. The baseline SDF level was higher in conventional frozen-thawed than in sex-sorted frozen-thawed spermatozoa samples; while the reverse occurred for the rSDF. The afore-mentioned result produced a crossover point between both dynamic tendencies of SDF for sex-sorted versus conventional samples. We defined this crossover point as the Crossover Positioning Time (CPT) or the time (in hours) where both curves crossover after a period of spermatozoa incubation at 37 °C. The point at which the CPT occurs could be used as an indicator of the rSDF for individual bulls after X- and Y-chromosome bearing spermatozoa selection. CPT values produced a window of SDF ranging between 24 h and 48 h in the present experiment. It is proposed that higher values for CPT are indicative of bulls presenting chromatin that is more resistant to the external stressors affecting spermatozoa DNA after spermatozoa sorting.