Developmental speed affects the cryotolerance of in vitro produced buffalo (Bubalus bubalis) embryos

The aim of this study was to evaluate whether the developmental speed affects the cryotolerance of in vitro produced buffalo embryos. In Experiment 1, abattoir-derived oocytes were in vitro matured, fertilized and cultured. The embryos produced by Say 7 of culture were vitrified at the tight morula (TM), early blastocyst (EBL), blastocyst (BL), expanded-blastocyst (XBL) and hatched-blastocyst (HBL) stage. The embryos were vitrified by cryotop in 16.5% ethylene glycol (EG) and 16.5% dimethyl sulfoxide (DMSO) and 0.5 M sucrose. Embryos were warmed in 0.25 M sucrose for 1 min and then in 0.15 M sucrose for 5 min and cultured in vitro for 24 h, to evaluate post-culture viability. In Experiment 2, ovum pick-up (OPU) was carried out on lactating buffaloes to produce embryos that were vitrified-warmed and transferred into synchronized recipients. The lowest (P<0.01) survival rates were recorded with TM (22.4%) and the highest (P<0.01) with HBL (84.5%), whereas intermediate results were observed with EBL, BL and XBL (54.5, 64.7, 67.9%, respectively). Pregnancy rate on both Days 25 and 45 was significantly higher (P<0.05) for faster (XBL and HBL) developing embryos (75.0% and 62.5%, respectively) than for the slower (TM, EBL and BL) developing counterparts (36.4% and 0, respectively). Interestingly, pregnancies to term were only recorded when HBL were transferred (20%). In conclusion, it was demonstrated that the chronology of development is a major factor affecting the cryotolerance of in vitro produced buffalo embryos.