Effects of Timing of Activation and Aging of Bovine Oocytes Fertilized by Intracytoplasmic Sperm Injection (ICSI) on Cleavage and Subsequent Embryonic Development In Vitro.

Abstract

In cattle, activation treatment after intracytoplasmic sperm injection (ICSI) is required to improve cleavage and development rates. The objectives of this study were to evaluate 1) the effect of timing of ethanol activation after ICSI on cleavage and subsequent development (experiment 1), and 2) the effect of aging of bovine oocytes fertilized by ICSI followed by ethanol activation treatment (experiment 2). In experiment 1, cleavage rates were significantly higher in the groups receiving activation treatment 2 or 4 h after ICSI (64% or 70%) than that in the non-activation group (41%). The blastocyst rate was also significantly higher in the group receiving activation treatment 4 h after ICSI (19%). In experiment 2, cleavage and blastocyst rates were significantly higher in 22 to 26 h matured sperm-injected oocytes than those in non-activation groups. On the other hand, cleavage rates in 28 and 30 h matured sperm-injected oocytes were similar regardless of activation treatment and were not different from those in 22 to 26 h matured bovine oocytes activated with ethanol. However, despite activation treatment blastocyst rates in the 30 h matured oocytes were significantly lower than those in 22 to 28 h matured oocytes activated with ethanol. These results indicate that the timing of activation treatment and the age of bovine oocytes affect the cleavage and subsequent development following ICSI.