Evaluation of estradiol benzoate as a pre-treatment for oocyte recovery in sheep

The objective of this study was to compare the number of follicles, oocytes and the recovery rate in sheep submitted to the one-shot protocol with or without ovarian priming with estradiol benzoate (EB). Pluriparous non-lactating sheep (n=33) with an average age of five years (range 4-6) and a body condition score of 3.0 +/- 0.3 were divided into three groups. The one-shot group (n=10) was treated with a subcutaneous implant containing 1.5 mg of norgestomet from D0 to D10. The animals in this group were administered 0.04 mg of D-cloprostenol, 200 IU of follicle stimulating hormone (FSH) and 300 IU of equine chorionic gonadotropin (eCG) on D8. Animals in the EB group (n=11) received the same treatment as one-shot plus the administration of 0.6 mg of EB on D0. In the untreated group (n=12), the animals received no hormone stimulation. The collection of the oocytes was performed by laparotomy 36 h after the administration of gonadotropins (D10). Oocytes were searched and classified based on morphology. An increase was observed (p<0.05) in the number of follicles aspirated in the one-shot vs. the EB and untreated groups (16.3 +/- 5.6 vs. 9.5 +/- 2.4 and 12.1 +/- 4.1), respectively. The average number of oocytes and the recovery rate were higher (p<0.05) in the one-shot and EB groups compared to the untreated group, resulting in 14.2 +/- 9.0 and 87.1% (142/163), 11.0 +/- 6.2 and 91.4% (122/134) vs. 6.8 +/- 3.5 and 71.9% (82/114), respectively. It was concluded that the EB did not improve efficiency in the one-shot protocol, but was significantly better than in untreated animals.