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Sex-related growth differences between male and female embryos remain an attractive subject for reproductive biologists. This study aimed to investigate the endogenous factors that play a crucial role in the pace of early development between male and female bovine embryos. Using sex pre-selected semen by Y-specific monoclonal antibodies for the production of bovine embryos, we characterized the critical endogenous factors that are responsible for creating the development differences, especially during the pre-implantation period between male and female embryos. Our results showed that at day seven, (57.8%) Y-sperm sorted in vitro cultured embryos reached the expanded blastocyst (BL) stage, whereas the X-sperm sorted group were only 25%. Y-BLs showed higher mRNA abundance of pluripotency and developmental competency regulators, such as Oct4 and IGF1-R. Interestingly, Y-sperm sorted BLs had a homogeneous mitochondrial distribution pattern, higher mitochondrial membrane potential (∆Ψ m ), efficient OXPHOS (oxidative phosphorylation) system and well-encountered production of ROS (reactive oxygen species) level. Moreover, Y-blastocysts (BLs) showed less utilization of glucose metabolism relative to the X-BLs group. Importantly, both sexes showed differences in the timing of epigenetic events. All these factors directly or indirectly orchestrate the whole embryonic progression and may help in the faster and better quality yield of BL in the Y-sperm sorted group compared to the X counterpart group.

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Serum has widely been used as a main supplement to embryo in vitro culture media as it contains embryotrophic factors. Charcoal:dextran treatment of fetal bovine serum (FBS) removes lipophilic chemicals and certain steroid hormones and growth factors. The objective of this study was to investigate the effects of charcoal:dextran-stripped fetal bovine serum (CDS FBS) and heat-inactivated FBS (HI FBS) in embryo culture medium (SOF-BE1 medium supplemented with 10% of serum) on their ability to support in vitro development of bovine embryos. The developmental ability and quality of bovine embryos were determined by assessing their cell number, lipid content, mitochondrial activity, gene expression, and cryo-tolerance. The experiment was conducted in 6 replicates (350 oocytes per group). The differences in embryo development, integrated optical intensity, and expression levels of the various genes between experimental groups were analysed by one-way ANOVA. Duncan’s multiple range tests were used to test the differences between the treatments. The level of statistical significance was set at P < 0.05. The percentages of embryos that underwent cleavage and formed a blastocyst were significantly (P < 0.05) higher in medium containing CDS FBS than in medium containing HI FBS (42.84 ± 0.78% v. 36.85 ± 0.89%, respectively). The total number of cells per Day 8 blastocyst was not significantly different (P > 0.05) between the CDS FBS group (208.40 ± 14.77) and the HI FBS group (195.11 ± 19.15). Furthermore, the beneficial effects of CDS FBS on embryos were associated with a significantly increased mitochondrial activity, as identified by MitoTracker Green, and reduced intracellular lipid content, as identified by Nile red staining, which increased their cryo-tolerance. The post-thaw survival rate of blastocysts was significantly (P < 0.05) higher after 24 h in the CDS FBS than in the HI FBS group (85.33 ± 4.84% v. 68.67 ± 1.20%). Quantitative reverse transcription PCR showed that the mRNA levels of lipid metabolism-related genes, acyl-CoA synthetase long-chain family member 3, acyl-coenzyme A dehydrogenase long-chain, and the cholesterol metabolism related gene hydroxymethylglutaryl-CoA reductase were significantly increased upon culture with CDS FBS. Moreover, the mRNA levels of survival gene sirtuin 1, antioxidant gene superoxide dismutase 2, and anti-apoptotic associated gene B-cell lymphoma 2 in frozen–thawed blastocysts were significantly (P < 0.05) higher in the CDS FBS group than in the HI FBS group; however, the mRNA level of the pro-apoptotic gene BCL2-associated X protein was significantly reduced. In conclusion, these data suggest that supplementation of in vitro culture medium with CDS FBS improves in vitro bovine embryo developmental competence and the quality of blastocysts in terms of their crytolerance and gene expression. This research was supported by grant from the Next-Generation BiogGeen21 (No. PJ01107703), IPET (No. 315017-5 and 117029-3), Allergy free cat (Co.. Felix Pets), BK21plus, and KGSP.