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
