The participatory relationship among the follicle size, follicle stimulating hormone (FSH), and cysteamine (antioxidant agent) contribute to the production of embryos characterized by abundance and good quality. The aim of this study was to evaluate the efficacy of FSH, cysteamine and follicle size on <em>in vitro</em> embryo production of Awassi sheep oocytes. Follicles sizes were determined into two groups: small follicles (1-2 mm) and large follicles (&gt; 2 mm). Oocytes were matured across two increasingly shared levels of FSH and cysteamine: A (40 ng/ml + 50 μM) and B (60 ng/ml + 100 μM). Results of the bilateral interaction showed significant differences across the follicle size (large follicles group) and the maturation treatment (B medium) in the rates of fertilization (highest value: 67.51%; p= 0.02), cleavage (highest value: 65.41%; p= 0.01), 2-16 cell stage (lowest value: 2.29%; p= 0.0001), blastocyst stage (highest value: 44.82%; p= 0.04), down to morula stage arrest (lowest value: 55.17%; p= 0.04) and Type I embryos (highest value: 52.87%; p= 0.03). Likewise, matured oocytes of small follicles group (B medium) attained the highest rate of morula stage (56.60%; p= 0.03). No significant differences were observed in Type II and Type III embryos. In order to obtain high yields of good quality embryos, it is advised to add FSH and cysteamine with levels of 60 ng/ml and 100 μM respectively to maturation medium of ovine oocytes obtained from follicles with a diameter &gt; 2 mm.

In this study, two experiments were conducted to study the effect of both the follicle size and the cryoprotectants dimethyl sulfoxide (DMSO) and ethylene glycol (EG) on the main phases of nuclear maturation (Experiment I), cleavage stages and embryo quality (Experiment II) of Awassi sheep oocytes. Follicles were classified into two groups: small follicles (SF) (1-2 mm) and large follicles (LF) (> 2 mm). Oocytes were vitrified in three solutions: A (30% DMSO), B (30% EG) and C (15% DMSO and 15% EG). In Experiment I, the resulting vitrified-thawed oocytes in solution C achieved the best rates after the control group (fresh), respectively as the rates of maturation, germinal vesicle (GV), metaphase II(M-II), arrest, and lyses were 85.71% (P = 0.04), 8.33% (P = 0.02), 72.92% (P = 0.04); LF group, 15.25% (P = 0.04), and 5.08% (P = 0.04); SF group, respectively. In Experiment II, the same group of oocytes achieved the best rates after the control group, as the rates of fertilization, cleavage, 2-16 cell, Type3, blastocyst, and Type1 embryos were 63.28% (P = 0.001), 57.46% (P = 0.001), 40.38% (P = 0.04), 38.46% (P = 0.04); LF group, 30.00% (P = 0.01), and SF group 36.67% (P = 0.001), respectively, while the vitrified-thawed oocytes in A solution (SF group) reached the highest rate of Type 2 embryo quality (58.06%; P = 0.01). No significant differences were noticed in the germinal vesicle breakdown (GVBD), metaphase I (M-I) and morula stage. Vitrification of oocytes obtained from follicles with a diameter of more than 2 mm in a cocktail solution of DMSO (15%) and EG (15%) led to a significant increase in the yield and quality of the resulting sheep embryos.