Ovarian follicular flushing as a means of increasing oocyte yield and in vitro embryo production in cattle

Context The number of developmentally competent cumulus-oocyte complexes (COCs) retrieved during Ovum Pick-Up (OPU) determines success in both bovine and human assisted reproduction. Follicular flushing for COC retrieval is practicsed widely in humans but not in cattle. Aims To determine the benefits of follicular flushing in cattle and assess the merits of a novel 16G double-lumen needle ('OxIVF') that flushes laterally to the needle shaft. Methods Experiment 1 flushed 655 antral follicles (≥7mm) from 255 abattoir-derived cattle ovaries. In Experiment 2, 12 Holstein heifers underwent two cycles of OPU in a cross-over design comparing both needle types. In Experiment 3, 11 Holstein heifers underwent two cycles of OPU using the OxIVF needle in a cross-over design: flushing (≥7mm follicles) vs a 'Hybrid' approach of flushing (≥7mm follicles) and aspiration (5-7mm follicles); followed by two cycles of standard follicle aspiration (>5mm follicles). Key results In Experiment 1, COC recovery was greater (P =0.034) for the OxIVF vs Standard needle (mean±s.e.; 74.1±2.10% vs 67.0±2.23%); yield of Grade 1 COCs was also greater (20.1±1.97% vs 8.2±1.38%; P P =0.045) for the OxIVF vs Standard needle (89.1±2.98% vs 79.6±3.47%). Day 6 embryo yield was also greater (P =0.017) for the OxIVF vs Standard needle (87.2±4.38% vs 67.6±6.73%). In Experiment 3, recovery of COCs was greater (P =0.033) for 'Flush' vs 'Aspirate' groups (82.1±5.06% vs 66.2±3.48%). However, number of Day 8 blastocysts for the 'Hybrid' vs 'Flush' approach (9.2±1.39vs 6.5±1.05 per cycle) did not reach statistical significance. Conclusions Follicular flushing using the OxIVF needle, embracing the 'Hybrid' approach, has the potential to increase oocyte retrieval and blastocyst number per donor cycle in cattle but requires further validation. Implications Larger scale studies will seek to confirm benefits of follicular flushing using the OxIVF needle in cattle. Future studies should consider applications in both equine and human assisted reproduction.