Oocyte quality determines bovine embryo development after fertilisation with hydrogen peroxide-stressed spermatozoa.

Exposure of gametes to specific stressors at sublethal levels can enhance the gametes' subsequent performance in processes such as cryopreservation. In the present study, bull spermatozoa were subjected to H₂O₂ for 4 h at 100-, 200- and 500-μM levels; computer-assisted sperm analysis (CASA) and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) assay were used for evaluation of subsequent sperm motility and DNA integrity, respectively. Exposure of spermatozoa to H₂O₂ did not affect sperm motility but DNA integrity was negatively affected by 500 μM H₂O₂ compared with mock-exposed spermatozoa, whereas both motility and DNA integrity were affected compared with untreated spermatozoa. Nevertheless, insemination of oocytes with spermatozoa exposed to 200 μM H₂O₂ increased fertilisation, cleavage and blastocyst rates (P < 0.05). Furthermore, the higher blastocyst yield after fertilisation of oocytes with spermatozoa exposed to 200 μM H₂O₂ was related to oocyte diameter, with large-medium oocytes yielding higher blastocyst rates, while small-diameter oocytes consistently failed to develop into blastocysts. In conclusion, the results indicate that exposure of spermatozoa to 200 μM H₂O₂ before sperm-oocyte interaction may enhance in vitro embryo production in cattle. However, this increased embryo production is largely dependent on the intrinsic quality of the oocytes.