Developmental Asynchrony during in vitro Culture of in vitro Matured and Fertilized (IVMF) Pre-pubertal and Adult Sheep Oocytes

In this study we compared cleavage rates (from 2-cell stage to hatched blastocyst) of IVMF oocytes derived from pre-pubertal (4–6 week old) or adult (2–6 year old) slaughtered sheep. Cumulus- oocyte complexes were matured and fertilized and two-cell stage embryos were collected at 22, 26, 40 h after fertilization and cultured separately in SOFaa + 0.4% bovine serum albumin for 9 days. Data were analysed by chi-squared test. IVMF oocytes from pre-pubertals reached the 2-cell stage 4 h later than those from adults (16.6, 24.3 and 59.2% vs 35.7, 33.9 and 30.4% at 22, 26 and > 26 h respectively, after fertilization). This delay increased up to one day by the blastocyst stage (d + 6 ¼ 0 vs 45.2%; d + 7 ¼ 47.5 vs 25.8%; d + 8 ¼ 39.3 vs 29% and d + 9 ¼ 13.1 vs 0% respectively, for pre-pubertal and adult). Fewer IVMF oocytes from pre-pubertals developed to the blastocyst stage compared to those derived from adults (18.0% vs 55.4%; p < 0.01) and hatching rate was reduced (34.4% vs 62%; p < 0.01). Hatching rate was higher ( p < 0.01) in quick developed blastocysts (85.7, 53.1 and 33.3% in adult at d+6, d+7 and d+8 respectively vs 55.1, 16.6 and 12.5% in prepubertal at d+7, d+8 and d+9 respectively). In conclusion, the lower competence of oocytes derived from pre-pubertals compared to adults was characterized by a delay in cleavage, blastocyst and hatching rates during in vitro culture. Supported by MIUR (Cofin).