The objectives were to determine the effects of addition of growth factor(s) and antioxidant to defined (DMM), semi-defined (SDMM), or undefined (UDMM) sheep oocyte maturation media on cleavage and subsequent embryo development. Exogenous epidermal growth factor (EGF, 10 ng mL^–1), insulin-like growth factor-I (IGF-I, 50 ng mL^–1), or cysteamine (Cys, 100 m) was added to DMM, SDMM, or UDMM. In the experiments, 967 oocytes were collected from 1160 ovaries (Experiment 1), 770 oocytes were collected from 831 ovaries (Experiment 2), and 778 oocytes were collected from 845 ovaries (Experiment 3). After in vitro fertilization with fresh ram semen in SOF medium, groups of 10 oocytes were stripped free of cumulus cells and transferred into 50 μL of a 2-step SOF medium. The incubations were conducted under paraffin oil at 38.5°C in a humidified atmosphere of 5% O₂, 5% CO₂, and 90% N₂. In all experiments, data were analyzed by ANOVA. Duncan’s multiple range test was used to determine the difference between 2 means after ANOVA. Results were expressed as mean ± SEM, and statistical significance was accepted from P < 0.05. In Experiment 1, the effects of IGF-I and EGF in DMM (TCM-199 supplemented with FSH, LH, 17β-estradiol, Na pyruvate, gentamycin sulfate, and polyvinyl alcohol) were evaluated in 4 treatment groups (DMM as a control, DMM + EGF, DMM + IGF-I, and DMM + EGF + IGF-I). Cleavage, morula, and blastocyst production rates were higher in the DMM + EGF + IGF-I (83.1 ± 0.5, 47.7 ± 0.5, and 30.8 ± 1.2) than in the DMM (72.9 ± 1.3, 37.0 ± 1.1, and 20.2 ± 1.2), DMM + EGF (77.2 ± 1.0, 43.2 ± 2.1, and 26.1 ± 1.8), or DMM + IGF-I (79.9 ± 0.6, 43.3 ± 1.2, and 25.7 ± 1.3) groups (P < 0.05). In Experiment 2, the effects of Cys in DMM were evaluated. The addition of Cys to DMM + EGF + IGF-I resulted in a mean blastocyst rate of 35.0 ± 0.9% compared with 31.5 ± 1.3% in DMM + EGF + IGF-I alone (P < 0.05); however, mean cleavage rates (84.5 ± 1.3 v. 82.8 ± 1.0) did not differ (P = 0.32). In Experiment 3, the effects of DMM + EGF + IGF-I + Cys, SDMM (TCM-199 supplemented with FSH, LH, 17β-estradiol, Na pyruvate, gentamycin sulfate, and BSA) + EGF + IGF-I + Cys, and UDMM (TCM-199 supplemented with FSH, LH, 17β-estradiol Na pyruvate, gentamycin sulfate, and FBS) + EGF + IGF-I + Cys on cleavage and embryo developmental were compared. The UDMM supplemented with EGF, IGF-I, and Cys resulted in higher proportions of cleavage, morula yields, and blastocyst yields (P < 0.05) than the DMM or SDMM supplemented with EGF + IGF-I + Cys. There was no significant difference between DMM and SDMM in the proportions of oocytes reaching the morula and blastocyst stages. In conclusion, an efficient system for in vitro production of sheep blastocysts was developed by using a defined oocyte maturation system combined with growth factors, hormones, and an antioxidant, but the UDMM resulted in higher cleavage, morula yields, and blastocyst yields than the DMM or SDMM.