EFFECTS OF PREINCUBATION AND INSEMINATION TIMES OF SPERMATOZOA ON THE DEVELOPMENT OF BOVINE OOCYTES FERTILIZED IN VITRO

Bovine in vitro fertilization experiment was carried out using ovary-derived follicular oocytes and frozen-thawed spermatozoa to determine the optimal preincubation time of spermatozoa and the insemination time for successful in vitro fertilization rate. The possibility of parthenogenetic cell division of unfertilized oocytes during culture without spermatozoa was also examined. There was no significant (p>0.05) difference in percent ratio of embryos developed to blastocyst stage between 0 and 3 h preincubation times of spermatozoa, showing a tendency to have higher percentage for 0 h of preincubation time. The 6 h insemination time seemed to be better for producing higher percentage of ova cleavage compared with those of 1 and 3 h treatments. Approximately 10% of unfertilized oocytes divided into 2 to 4-cell stage, and some of them cleaved to 5 up to 8-cells. The results obtained from this study suggested that 0 h of sperm preincubation time and 6 h of insemination time would be suitable for producing better in vitro fertilization rate of bovine oocytes. It is also likely that unfertilized bovine oocytes probably cleave to some cell stages with irregular divisions of the cells. On the one hand, considerable variation was also found in spermatozoa function among individual bulls.