Synergistic Effect of Insulin on in vitro Development of Immature Bovine Oocytes

Abstract

Problem statement: Development of efficient culture system to support embryonic development would be valuable when quality of produced embryos was important. However, the rate of bovine embryo production in vitro was still lower than expected. Present study, including of three experiments, was carried out to investigate the effect of insulin on nuclear maturation and subsequent development of immature bovine oocytes and in vitro fertilized embryos. Approach: Grade one cumulus-oocyte-complexes harvested from slaughterhouse ovaries were selected and randomly allocated in each treatment groups. In experiment 1, in vitro maturation medium (Hepes-buffered medium 199 + fetal calf serum + gonadotrophins + antibiotics) supplemented with 0 (control), 1, 10, 20 and 100 μg mL^-1 of insulin. In experiment 2, to eliminate the effect of serum and hormones, Hepes-buffered medium 199 was supplemented with 1 mg mL^-1 polyvinyl alcohols (PVA) and same levels of insulin. In experiment 3, the effect of insulin on bovine in vitro embryo development was assessed. Presumptive zygotes were randomly cultured in synthetic oviductal fluid added with 0 (control), 1, 10, 20 and 100 μg mL^-1 of insulin. Results: In experiment 1, nuclear maturation and embryo development rates were significantly higher in 1 and 10 μg mL^-1 compared with other groups (P<0.05). In experiment 2, both maturation and cleavage rate significantly increased in 1 and 10 μg mL^-1 insulin. The only treatment resulted in higher hatchability was 10 μg mL^-1 insulin (17.1±2.34%) compared with control (11.34±3.94). In experiment 3, cleavage and morula rates were significantly greater in 1 and 10 μg mL^-1 insulin compared with other groups; although the highest rates resulted by using 10 μg mL^-1. Conclusion: Obtained results show that inclusion of 10 μg mL-1 insulin in maturation and culture medium exerted beneficial effects on nuclear maturation of bovine oocytes and in vitro embryo development till morula stage.