Influence of oocyte recovery method, in vitro fertilization method and serum source on embryonic development of in vitro matured bovine oocytes

The objective of this study was to investigate the influence of various factors on blastocyst development in a bovine in vitro embryo production system. Two production systems were originally compared: Protocol 1, which utilized oocyte recovery by slicing, 20 % fetal bovine serum with FSH (FBS+) for oocyte maturation, and sperm preparation system 1 (F1), and Protocol 2, which utilized oocyte recovery by aspiration, 5 % estrous cow serum with FSH, HCG and estradiol (ECS+) for oocyte maturation, and sperm preparation system 2 (F2). Because a significantly higher blastocyst development rate was found for Protocol 2, the different factors of oocyte recovery technique (slicing vs. aspiration), sperm preparation technique (F1 vs. F2) and serum and hormone supplementation during maturation (FBS+ vs. ECS+) were evaluated. Recovering oocytes using the alternative technique (slicing vs. aspiration) did not significantly alter blastocyst rate on Day 8 within either production system 1 (FBS+/F1) or production system 2 (ECS+/F2). Although investigations of influence of the type of fertilization method revealed no effect, a significant effect of the type of serum was observed on the blastocyst rates with ECS+ proving better as compared to the use of FBS+ (P<0.03). When embryos produced from these investigations were evaluated by differential staining, the number of ICM cells did not differ among treatment, but the number of TE cells, and thus the total cell number, and the ICM : TCN ratio, was significantly increased when oocytes were matured in ECS+ supplemented medium, regardless of sperm preparation method. In conclusion, serum supplementation, but not oocyte recovery method or sperm preparation method, was responsible for the difference in blastocyst rate between the two original IVP protocols.