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Poor development of oocytes from prepubertal animals is a major factor that hinders the application of the technology, juvenile in vitro embryo transfer (JIVET). The aim of this study was to explore the possibility of improving the developmental competence of prepubertal oocytes by supplementing the oocyte in vitro maturation (IVM) medium with antioxidants and cytokines. Effects of two antioxidants, melatonin and sericin, were first examined. The results showed that melatonin had no significant beneficial roles on the lamb oocyte development, while 0.5% sericin supplemented during IVM significantly increased the blastocyst rate of lamb oocytes (46.5% vs 19.2% in control, P < 0.05). Next, effects of two kinds of combined supplements, insulin-transferrin-selenium (ITS) and fibroblast growth factor 2(FGF2)-leukemia inhibitory factor (LIF)-insulin-like growth factor1 (IGF1)(FLI) were tested. The results indicated that addition of FLI, but not ITS, in the IVM medium, significantly improved the blastocyst development of lamb oocytes (43.9% in FLI group vs 21.6% in control, P < 0.05). Further comparison showed that the developmental competence of oocytes was not significantly different among supplementation with sericin or FLI alone or both, all of which generated similar outcomes of blastocyst yield to the supplementation with adult follicular fluid. Finally, 27 blastocysts produced from lamb oocytes matured in the presence of sericin and FLI were transferred into 18 recipients, of which 9 were pregnant. This study suggests that the developmental competence of prepubertal oocytes can be improved by supplementing IVM medium with relevant agents like sericin and cytokines. • Sericin supplementation during IVM improves the lamb oocyte developmental competence. • FLI supplementation during IVM improves the lamb oocyte developmental competence. • Melatonin and ITS have no beneficial roles on the lamb oocyte development. • The developmental competence of prepubertal oocytes can be improved by modifying IVM medium. [ABSTRACT FROM AUTHOR]

Abstract Oocytes from prepubertal lambs have lower developmental ability than that from adult ewes. Follicular fluid (FF) provides an important microenvironment for oocyte development and maturation in vivo. The aim of this study was to examine the effects of FF supplemented during in vitro maturation (IVM) on the developmental competence of prepubertal lamb oocytes. FF was collected from follicle-stimulating hormone (FSH) stimulated adult ewes or 4‒6-week-old lambs or abattoir-derived adult ovaries. The FF was supplemented to the control IVM medium, TCM199 containing 20% estrus sheep serum and hormones. It was found that the lamb oocytes matured in medium supplemented with 20% or 30% adult FF from FSH-stimulated ewes yielded significantly higher blastocyst rates than that from the control medium, or medium supplemented with 10% adult FF or 20% lamb FF (43.5%, 37.9% vs. 28.4%, 29.7%, 27.6%, P < 0.05). However, when adult oocytes were matured in medium supplemented with 20% adult FF, their cleavage and blastocyst development were similar to that of those matured in control medium. Addition of 20% adult FF from abattoir-derived ovaries to IVM medium also significantly increased the blastocyst formation of lamb oocytes when compared to that from the medium without FF supplementation. The blastocyst development did not differ between the groups of FF from abattoir-derived ovaries and from FSH-stimulated ewes (38.2% vs 43.1%, P > 0.05). A total of 146 blastocysts derived from different groups of lamb oocytes were transferred into 76 synchronized recipients, of which 50% were pregnant and 38.2% lambed. These results suggest that supplementing IVM medium with adult FF has beneficial roles on the developmental competence of prepubertal lamb oocytes. Highlights • Adult follicular fluid improves the developmental competence of prepubertal lamb oocytes in vitro. • Adult follicular fluid has no effect on the developmental competence of adult ewe oocytes in vitro. • Lamb follicular fluid has no inhibitory effect on development of oocytes in vitro. • Full-term development of embryos produced from lamb oocytes was evaluated. [ABSTRACT FROM AUTHOR]