Effects of β-mercaptoethanol on formation of pronuclei and developmental competence of swamp buffalo oocytes

This study was conducted to determine the effect of supplementing maturation medium with β-mercaptoethanol (βME) on pronuclei formation and developmental competence of swamp buffalo oocytes. Buffalo oocytes were matured in TCM199 medium either with 10 mM βME or without βME supplementation for 24 h. In Experiment 1, oocytes were fixed and stained for cytological evaluation after in vitro fertilization (IVF). In Experiment 2, presumptive zygotes were cultured and their developmental competency was assessed. It was found that βME significantly improved the proportion of oocytes that exhibited synchronous pronuclei formation (31.8±5.1% versus 17.9±3.3%, P<0.05). There were no significant differences between oocytes matured with or without βME in their capability of developing into blastocyst-stage embryos (3.0±1.3% versus 1.8±0.9%). However, blastocysts produced from oocytes matured in the presence of βME appeared to develop faster than those from oocytes matured in the absence of βME (P<0.05). Cavitation of embryos from oocytes matured in the presence of βME occurred at 156 hpi, whereas those matured in the absence of βME occurred at 180 hpi. Although in vitro production of blastocysts did not increase by addition of βME to maturation medium, quality of blastocysts produced from oocytes matured in the presence of βME was improved. This study provides information for further investigations on optimizing a system for in vitro production of swamp buffalo embryos.