The effect of follicle size and cryoprotectants on nuclear maturation and early embryonic development of vitrified - thawed Awassi sheep oocytes (Ovis aries)

Abstract

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.

Novelties in Ovine Assisted Reproductive Technologies – A Review

“…The in vitro maturation (IVM) of oocytes includes alterations of both the cytoplasm and nucleus in a synchronous manner. The oocyte heterogeneity in quality can be a source of high variability in IVM maturation but in most instances the success in reaching metaphase II can be higher than 80% in sheep (57,58). Oocytes are conventionally placed in IVM medium in groups of 25-50 and incubated at 38-39 °C for 24-27 hours in 5% CO 2 atmosphere (59).…”

Evaluation of the In Vitro Embryo Production of Farm Animals Under the Circumstances of Embryo Transfer Technology

“…In this regard, more research has been conducted by relying on innovative technologies and methods, the most important of which is the technique of in vitro embryo production (IVEP). It can be said that the IVEP technology has achieved a significant harvest in the yield of the produced embryos despite the difficulties encountered and the relatively low productivity levels of these embryos [5][6][7][8]. In the current period, the integrated protocols in which many additives and improved culture media were used have eventually led to noticeable differences in the outcome of embryos produced.…”