L-carnitine improved bovine blastocyst rate and quality when supplemented at different preimplantation stages

The present study investigated the effect ofL-carnitine supplementation during different pre-implantation stages on bovine embryo development rate and quality. Good morphologically cumulus-oocyte complexes (n=2126) recovered from slaughterhouse ovaries were matured, fertilized in vitro and presumed zygotes were further cultured in vitro (IVC) in CR1-aa media till day 8. For the setup of the study, L-carnitine (1.5 mM) was added at different technological steps (IVM, IVF, IVC and all stages) and different developmental stages (early IVC: 1to 4-cell vs. late IVC: 8-cellembryos). Moreover, untreated (control) group was also included in this experiment.Quality of embryos developed from all experimental groupswere evaluated usingterminal deoxynucleotidy ltransferased UTP nick end labeling (TUNEL) assay which assesses total normal and apoptotic cell numbers ofembryos. Real-time PCR was used to profile 5 embryo marker genes (SOD2, CDX2, IFNt, Glut8 and TFAM) in addition; GAPDH was used as housekeeping gene. Results of the current study showed a significant increase in blastocyst rate at day 8 of culture when Lcarnitine was added at IVM (34.1±2.6), early IVC (34.6±1.7), late IVC (38.4±2.8), and all stages (36.4±3.5) compared to control (22.5±1.4) and IVF (26.0±1.1) groups.The blastocyst total number of cells was greater (P < 0.05) in groups that L-carnitine was added at IVM (134.1±4.9), IVF (125.7±2.8), early IVC (133.8±5.7), late IVC (139.2±3.5) and all stages (137.0±4.1) compared to control (115.3±3.6). On the other hand, control embryo group has more apoptotic cells (10.4±1.9) than L-carnitine treated groups at IVM (4.1±1.2), IVF (5.5±1.6), early IVC (3.9±1.4), late IVC (4.0±1.7) and all stages (2.8±2.0). The expression profile of SOD2, IFNt, Glut8 and TFAM genes was increased in embryos treated with L-carnitine at IVM, early IVC, late IVC and all stages compared to IVF and control groups. In addition, CDX2 transcript was more abundant in IVM, late IVC and all stages treated groups than in any other embryo group. Overall, the findings of the present study support the notion that L-carnitinecould be a potential antioxidant substance that has a positive effect on embryo development rate and quality when supplemented to all culture media throughout bovine preimplantation.