Ovum pick up in swine: the influence of aspiration vacuum pressure on oocyte recovery from preovulatory follicles.

Endoscopical ovum pick up (OPU) in swine is a minimal invasive and reliable technique to aspirate oocytes from preovulatory follicles for studying intrafollicular development and oocyte maturation as well as for IVM/IVF-programs. The aim of the present study was to determine the effect of different aspiration vacuum pressures on oocyte recovery and on the morphology of cumulus oocyte complexes (COCs). Oestrus of crossbred Landrace gilts (n = 33) was synchronized by feeding altrenogest and follicular growth was stimulated with 1,000 IU PMSG 24 h after the last altrenogest application. On day 4 after PMSG application preovulatory healthy follicles of > 5 mm diameter were aspirated laparoscopically. Aspiration was carried out using a two-way cannula and an electronic aspiration pump. Five different vacuum pressures were used: 10, 17, 32, 47 and 66 ml water/min, corresponding to 30, 60, 125, 250 and 375 mm Hg, respectively. Fluids from different follicles were pooled per ovary and the morphology of cumulus oocyte complexes (COCs) was determined microscopically immediately after aspiration. COCs were classified into oocytes with intact cumulus (i.e. compact or slightly expanded COC), oocytes with corona radiata and denuded oocytes. A total of 695 follicles were aspirated and 501 COCs recovered. Increasing the aspiration pressure stepwise from 10 ml water/min up to 66 ml water/min resulted in a decrease in oocyte recovery rate. A significant higher (P < 0.05) rate of oocyte recovery (77.4% v.s. 59.8%) was achieved using a vacuum pressure of 17 ml water/min compared to 66 ml water/min, respectively. There was a tendency to reduce the portion of COCs with intact cumulus from 82 to 88% to 77% if the vacuum pressure increased to more than 47 ml water/min. A higher aspiration pressure provoked an increase (P < 0.05) in the number of denuded oocytes: 0 to 3% at 10 to 32 ml water/min, respectively, compared to 10% at 47 ml water/min to 17% at 66 ml water/min. These results demonstrate that variation in aspiration pressure affects oocyte recovery rate and COC quality. Aspiration vacuum pressure of 17 to 32 ml water/min was found to be optimal in swine both for oocyte recovery and COC quality.