The effect of vitrification device and embryonic stage on survival and developmental competence of Gabali rabbit embryos

Abstract

The current study aimed to evaluate the effect of vitrification device (straw or cryotop) and embryonic stage (pronuclear or morula stages) on survivability, normality and embryo development rate into blastocysts/hatched blastocysts. A total of 24 mature rabbit does of Gabali breed (5-6 months of age, 3-3.5 kg live body weight) were used in this study as embryo donors. Rabbit does were super ovulated by PMSG and hCG. Embryos at pronuclear stage including 4-cell and 8-cell embryos were recovered by flushing oviducts 30-34 h and 40-46 h post-mating, while, embryos at late morula stage were recovered by flushing oviducts 72 h post-mating. Embryos were vitrified by straw or cryotop. Survival and normality rates were determined. The vitrified embryos were in vitro cultured for 5 days to record blastocyst and hatching blastocyst formation rates. Results showed insignificant differences in survival and normality rates of vitrified embryos as affected by embryonic stage, although there were a tendency of higher rates yielded from embryos at morula than at pronuclear stage (87.7 and 89.2% vs. 85.9 and 85.2%, respectively). Survival and normality rates were higher (P<0.05) using cryotop than straw, being 92.1 and 93.1% using cryotop versus 81.7 and 81.0% using straw, respectively. Expansion and hatching rates were higher (P<0.05) for vitrified embryos at morula than at pronuclear stage (80.0 and 71.5% vs. 66.0 and 54.0%, respectively) and using cryotop than straw (81.6 and 75.3 vs. 63.1 and 48.2%, respectively). It can be concluded that the feasibility of using the cryotop method to vitrify rabbit embryos rather than straw method at various developmental stages, particularly at morula stage.