Effect of 2-mercaptoethanol and cysteine supplementation during in vitro maturation on the developmental competence of oocytes from hormone-stimulated lambs

Abstract

The objective was to determine the effect of 2-mercaptoethanol and cysteine on in vitro developmental competence of oocytes from lambs (4–8-week old) stimulated with eCG and pFSH. Oocytes were matured in medium (TCM199) with no supplement (Control group) or with 100 μM 2-mercaptoethanol and 600 μM cysteine (GSH group). Oocytes from adult sheep were also included (Adult group). The addition of 2-mercaptoethanol and cysteine did not improve nuclear maturation or microtubule configuration 12, 15, 18, or 24 h after placement in maturation medium. Sperm head decondensation and male pronucleus formation were evaluated at 6, 12, and 18 h after commencement of IVF; sperm decondensation appeared earlier in the GSH group (6 h after the start of IVF). There were differences ( P < 0.05) between the Control group and the GSH and Adult groups for: fertilization rate at both 12 h (55.4, 77.0, and 80.6%, respectively) and 18 h (67.9, 86.9, and 88.7%); parthenogenesis rate at both 12 h (25.0, 10.8, and 5.6%) and 18 h (28.3, 9.8, and 4.5%); and polyspermy rate at 18 h (26.4, 4.9, and 5.7%). Blastocyst rate at 7 d was higher in the GSH group than the Control group (23.9% vs. 14.9%, P < 0.05), but both were lower ( P < 0.05) than the Adult group (38.3%). The addition of 2-mercaptoethanol and cysteine improved sperm decondensation and rates of fertilization and the blastocyst development to 7 d, with no effect on blastocyst rate at 9 d.