In vitro maturation using αMEM with reduced NaCl enhances maturation and developmental competence of pig oocytes after somatic cell nuclear transfer

Background: Compared to medium containing 108 mM sodium chloride (NaCl), in vitro maturation (IVM) using a simple medium with reduced (61.6 mM) NaCl increases the cytoplasmic maturation and embryonic development of pig oocytes. Objectives: This study determines the effect of a complex medium containing reduced NaCl on the IVM and embryonic development of pig oocytes. Methods: Pig oocytes were matured in Minimum Essential Medium Eagle-alpha modification (alpha MEM) supplemented with 61.6 (61 alpha MEM) or 108 (108 alpha MEM) mM NaCl, and containing polyvinyl alcohol (PVA) (alpha MEMP) or pig follicular fluid (PFF) (alpha MEMF). Medium-199 (M199) served as the control for conventional IVM. Cumulus cell expansion, nuclear maturation, intra-oocyte glutathione (GSH) contents, size of perivitelline space (PVS), and embryonic development after parthenogenesis (PA) and somatic cell nuclear transfer (SCNT) were evaluated after IVM. Results: Regardless of PVA or PFF supplementation, oocytes matured in 61 alpha MEM showed increased intra-oocyte GSH contents and width of PVS (p < 0.05), as well as increased blastocyst formation (p < 0.05) after PA and SCNT, as compared to oocytes matured in 108 alpha MEMP and M199. Under conditions of PFF-enriched alpha MEM, SCNT oocytes matured in 61 alpha MEMF showed higher blastocyst formation (p < 0.05), compared to maturation in 108 alpha MEMF and M199, whereas PA cultured oocytes showed no significant difference. Conclusions: IVM in alpha MEM supplemented with reduced NaCl (61.6 mM) enhances the embryonic developmental competence subsequent to PA and SCNT, which attributes toward improved oocyte maturation.