EFFECTS OF QUALITY AND DEVELOPMENTAL STAGE ON THE SURVIVAL OF IVF-DERIVED BOVINE BLASTOCYSTS CULTURED IN-VITRO AFTER FREEZING AND THAWING

Factors affecting viability of IVF-derived bovine blastocysts after fr eezing and thawing were investigated. A total of 1,101 ova matured and fertilized in vitro were cultured under 2 different conditions, 1) in TCM-199 on granulosa cell monolayers at 5% CO2 in air and 2) in synth etic oviduct fluid (SOF) medium without somatic cell support at 5% CO2 , 5% O-2, 90% N-2. All blastocysts that developed from the 2 different culture systems were individually classified into 4 grades of embryo quality and were then frozen by conventional slow freezing. Developmen tal rates of the IVF-derived ova to blastocysts and the survival rates of the frozen-thawed blastocysts were not different between the SOF m edium (16 and 49%) and the co-culture system (13 and 61%, respectively ). Survival of frozen-thawed blastocysts was affected by embryo qualit y in both the SOF and co-culture systems (P<0.001). Blastocysts produc ed in vitro were also individually classified into 3 developmental sta ges and were then cultured for 3 d in the co-culture system with granu losa cells after freezing and thawing. There was a difference in the s urvival rate of frozen-thawed embryos between blastocyst developmental stages (early vs mid, P<0.05; mid vs expanded, P<0.01; early vs expan ded, P<0.001). The post-thawing survival rate of blastocysts frozen at Day 7 (62%) of culture was higher compared with that of Day 8 (45%), but there was no difference in survival rate between Day 7 and 8 of cu lture. The results indicate that the quality and developmental stage o f blastocysts are important factors influencing their survival after f reezing and thawing.