The Influence of Aspiration Pressure, Follicle Flushing Method and Needle Rotation During Single-Operator Opu Technique on Oocyte Recovery and Embryo Production in the Mare

The objectives of this study were to determine the effect of two aspiration pressures (75 vs 150 mmHg), the follicle flushing method (injection pump controlled by a foot pedal vs. a plastic syringe) and the twisting of the OPU needle on oocyte recovery and in vitro embryo production. A total of 104 warmblood sport mares belonging to a commercial OPU-ICSI program were used in a randomized clinical trial split in three experiments. In Experiment 1, mares were aspirated using either a high aspiration pressure (flow rate of 1.33 mL/sec; n=18) or low aspiration pressure (0.75 mL/sec; n=18); In Experiment 2, follicles were flushed either using a manual method (plastic syringe, n=18) or an automatic method (injection pump controlled by a foot pedal, n=18); and in Experiment 3, the follicles were aspirated by scraping of follicle wall with needle rotation (needle twisting, n=16) or without rotating the needle (control, n=16). In all experiments the same OPU operator and technician searching oocytes were used, and the experimental design was a randomized clinical trial. The overall mean oocyte recovery rate of the study was 54.2±17.1%, and the mean number of embryos per OPU-ICSI session was 1.9±1.6. The oocyte recovery rate was not influenced by any of the parameters investigated (P>0.05). However, the high aspiration pressure (150 mmHg) tended to yield oocytes with lower maturation (51.6%; P=0.09) and blastocyst rate (20.6%; P=0.08) following IVM and ICSI respectively, compared with the low aspiration group (64.4% MII rate and 31.4% blastocyst rate). In conclusion, there is no advantage of increasing the aspiration pressure to increase oocyte recovery. Furthermore, when a single operator performs the OPU (holding ovary and handling needle simultaneously), needle rotation to scrape the follicle wall does not improve oocyte recovery.