Effect of recovery method on yield of bovine oocytes per ovary and their developmental competence after maturation, fertilization and culture in vitro.

An important aim of an oocyte recovery method is to maximize the number of oocytes per ovary which can be employed for in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC). In this study, primary bovine oocytes were collected by 2 methods: aspiration of visible follicles (2 to 6mm in diameter) or surface dissection in which the ovary surface is finely dissected. The oocytes were classified on the basis of cumulus cover and cytoplasmic appearance. The total number of oocytes and the yield of good-quality oocytes recovered per ovary by surface dissection and aspiration were 44.2 and 13.9 and 13.5 and 4.6 (P<0.05), respectively. When a sample group of selected oocytes recovered by each method was measured, no significant difference was found in the mean diameter (144.11m vs 142.54m). A representative sample of good-quality oocytes recovered by each method was put through the IVM/IVF/IVC procedure: no significant difference in cleavage rate, cleavage index or blastocyst yield was found. However, when the blastocyst yield was compared on a per ovary basis, a significant difference was observed in favor of surface dissection (3.30+/-0.46 vs 0.96+/-0.16;P<0.05). When unselected oocytes recovered by surface dissection of the ovaries were put through the standard embryo production system, an average of 15.4 blastocysts per dam was obtained.