229 EVALUATION OF OOCYTE QUALITY RECOVERED FROM Gir BREED COWS WITH SYNCHRONIZED FOLLICULAR WAVE ON IN VITRO EMBRYO PRODUCTION

Abstract

Recent data reveal that approximately 80% of bovine embryos produced in vitro worldwide are from (Brazil J. H. M. Viana, personal communication). Adoption of this biotechnology by Brazilian producers might be attributed to particularities of the Bos indicus subspecies. Zebu breeds provide 2 to 3 times more viable oocytes than Bos taurus breeds per ovum pickup (OPU) session. This work aimed to evaluate the quality of cumulus–oocyte complexes (COC) retrieved from Gir breed cows (B. indicus) by OPU with a synchronized follicular wave and subjected to an in vitro embryo production (IVP) technique. All COC were obtained by OPU of 14 Gir cows performed every 14 days. There were 4 OPU sessions, preceded by synchronization of the follicular waves. Wave synchronization was achieved by an injection of 2 mg of oestradiol benzoate followed by the insertion of a norgestomet implant that stayed in place for 5 days. On Day 5, follicles of 2 to 8 mm were aspirated. The oocytes recovered were distributed according to classification: Group 1, with ≥3 cumulus cell layers and homogeneous or slightly heterogeneous cytoplasm (n = 314); and Group 2, ≤2 cumulus cells layers and slightly or coarsely granulated cytoplasm (n = 236). Oocytes from both groups were followed to in vitro maturation–IVF–fertilization–in vitro culture. Two (Day 2) and 8 (Day 8) days after the beginning of fertilization, the cleavage and blastocyst rates were measured, respectively. The statistical analyses were performed using a chi-square test (P < 0.05). The mean cleavage rates observed were 72.93 and 69.07% (not significant), whereas the mean blastocyst rates were 37.90 and 17.80%, and were significantly different for Groups 1 and 2, respectively. The results suggest that the morphology of oocytes (number of cumulus cell layers and cytoplasm homogeneity) is a strong indicator of the in vitro developmental capacity of oocytes recovered from Gir cows with synchronized follicular waves, although we did not observe compromised cleavage rates.