LAUSR

In vitro-produced (IVP) bovine embryos suffer from damage due to suboptimal culture conditions involving altered metabolism, reactive oxygen species generation and high lipid accumulation, which could be impacted by oocyte maturation × embryo culture interaction. We hypothesised that optimizing oocyte and embryo culture conditions would lead to a higher post-thaw embryo survival rate. The experiment was replicated 9 times in a factorial design with 3 oocyte maturation media: TCM-199 plus 10% serum and gonadotropins (control), BO-HEPES-IVM (BO, IVF Bioscience UK), and HMM (HEPES-buffered maturation medium) and 3 embryo culture media: BO-IVC (BOC), BBH7 (Cooley Biotech, Gainesville, FL, USA), and SCF1 (SOF for Conventional Freezing 1; Owen et al. 2017 Reprod Fertil Dev. 29, 129-130). Bovine oocytes (n = 2907) were aspirated from 2- to 8-mm follicles of abattoir ovaries, matured at 38.5°C for 22 to 24 h in 5% CO2 (control) or in BO and HMM in air, fertilized with semen from 1 of 3 bulls, and cultured in BOC, BBH7, and SCF1 at 38.5°C in 5.5% CO2, 5% O2, and 90% N2. Cleavage and blastocyst rates were evaluated at Day 3 and 7, respectively, after IVF. Selected stage 7 blastocysts were slow frozen using 1.5 M ethylene glycol supplemented with 1 mm l-ascorbic acid for 20 min (equilibration). The embryos were cooled to and seeded at –6°C, and then cooled to −32°C at 0.5°C/min. Embryos were thawed and re-expansion was assessed at 24 and 48 h. Data (Table 1) was arcsin transformed and analysed by ANOVA, and means separated by l.s.d. Results indicate that oocytes matured in BO and embryos cultured in SCF1 had a higher blastocyst rate than all oocytes matured in control medium and all embryos cultured in BBH7 (P < 0.05). However, oocytes matured in control medium and embryos cultured in BOC had lower post-thaw re-expansion rates than other treatment groups (P < 0.05). These results suggest that a combination of oocyte maturation and embryo culture media plays an important role in post-thaw embryo survival, al though interactions of present treatments need to be further evaluated. Table 1.Effect of maturation and culture media on blastocyst rate and cryotolerance ± SEM)