Effect of cryopreservation on sperm chromatin integrity and fertilizing potential in bovine semen

The present study was conducted on 83 bulls belonging to three species/breeds (Karan Fries crossbred and Sahiwal purebred cattle and Murrah buffalo). The bulls were selected based on their unacceptable semen parameters (poor semen quality and freezability) for comparative analysis with control bulls for assessing uncompensable seminal parameters, namely, detection of sperm chromatin maturity (using acidic aniline blue staining) and fragmentation level (comet assay of sperm nuclear DNA) along with production of 8-hydroxy-2′-deoxyguanosine (8-OHdG) (detected by high performance liquid chromatography of 8-OHdG) in cryopreserved semen specimen. The acidic aniline blue assay revealed that neither the fertility groups nor the species/breeds differed significantly, however, for comet assay only the fertility groups differed significantly (P < 0.05). High performance liquid chromatography analysis could detect the presence of the adduct (8-OHdG) in semen specimen of only three cattle breeding bulls. The results suggest that weekly collection of semen does not induce immature sperm production in dairy bulls. The cryopreservation of semen induces sperm DNA fragmentation which is comparatively higher in that of bulls with poor semen quality. 8-OHdG was not significantly produced and thereby is not a matter of serious concern for dairy bulls reared under stall-fed condition. It can be concluded that comet assay may be used for quality assessment of the cryopreserved semen samples especially which are to be used for inseminating the elite cows or for assisted reproduction.