Factors affecting recovery and quality of oocytes for bovine embryo production in vitro using ovum pick-up technology

In Experiment 1, different Vacuum pressures (30, 50, 70 and 90 mm Hg) were used to aspirate 4156 bovine follicles in vitro, to assess their effect on flow rate and the recovery, morphology and blastocyst formation of the reco vered oocytes. Cumulus oocyte complexes (COCs) were classified according to the morphology of the cumulus cells. Data were analyzed using Chi Square a nalysis. Overall recovery rate declined as the aspiration pressure increase d above 50 mm Hg (P<0.05). The recovery rate of Grade I oocytes decreased s ignificantly (P<0.05) as the vacuum pressure increased with a corresponding increase in the number of denuded oocytes recovered (P<0.05). The blastocy st yield, expressed as a percentage of recovered COCs decreased significant ly as the aspiration pressure increased beyond 50 mm Hg (P<0.05). In Experi ment 2, the holding media (hepes- or bicarbonate-buffered TCM 199) and hold ing time (1 h or 5 h) did not affect the blastocyst formation of the oocyte s (P>0.05). In Experiment 3, it was found that individual culture of the oo cyte during fertilization or culture had a detrimental effect on the oocyte s blastocyst formation (8.8% to 16% blastocyst yield on Day 8) when compare d to control (31.3%). In Experiment 4, groups of 5, 10 and 25 oocytes were compared with singly cultured oocytes. There were no significant difference s (P<0.05) in the blastocyst formation rate among groups of 5, 10, or 25 oo cytes, but there was a significant difference between oocytes processed in groups and those processed individually. In Experiment 5, when groups of 10 oocytes were cultured in different drop sizes, there was no significant di fference in cleavage rates between oocytes cultured in 100 mu L (85.0%, n = 280) and in 10 mu L (86.8%, n = 280) of media, but culture in 50 mu L (79. 3%, n = 280) resulted in cleavage rates significantly lower (P<0.05) than c ulture in 10 mu L drops. There was no significant difference in the blastoc yst formation. However there was a significant difference (P<0.05) in cell numbers of Day 8 blastocysts, with oocytes cultured in 100 mu L drops havin g significantly lower cell counts than oocytes cultured in 50 or 10 mu L dr ops. (C) 2000 by Elsevier Science Inc.