Frozen-thawed rhinoceros sperm exhibit DNA damage shortly after thawing when assessed by the sperm chromatin dispersion assay

This study reports on the successful validation (via in situ nick translation and neutral comet assay) of the equine Sperm-Halomax kit as an appropriate methodology for the assessment of sperm DNA fragmentation in three species of rhinoceros. Rhinoceros sperm nuclei with fragmented DNA (validated using in situ nick translation) were evident as large halos with dispersed DNA fragments, whereas those with nonfragmented DNA displayed small halos of nondispersed DNA within the microgel. There was a high correlation (r) of 0.974 (R2 value = 0.949; P < 0.01; n = 16) between the respective assessments of the Sperm Chromatin Dispersion test (SCDt) and the neutral comet assay. Application of the SCDt to determine the DNA fragmentation dynamics of rhinoceros (n = 6) sperm frozen in liquid nitrogen vapor and incubated postthaw at 37 °C for up to 48 h to mimic in vitro conditions in the female reproductive tract, revealed an increase (P = 0.001) in DNA damage, as soon as 4 h after the start of incubation. Linear regression equations were calculated for all six rhinoceroses over the first 6 h of incubation and revealed individual animal variation. Freshly collected and incubated (37 °C) rhinoceros (n = 3) sperm had no increase in the basal level of DNA fragmentation for up to 48 h, indicating that the cryopreservation of rhinoceros sperm in liquid nitrogen vapor, as used in this study, appeared to result in freeze-thaw DNA damage.