Vitrification of in vitro produced goat blastocysts: effects of oocyte donor age and development stage

This study examines the effectiveness of the cryotop vitrification method for the cryopreservation of goat blastocysts. To determine the effects of embryo development stage and donor age on in vitro survival rates, good-quality blastocysts from adult and prepubertal goats were sorted into non-expanded, expanded, hatching and completely hatched. In vitro produced (IVP) blastocysts were derived from prepubertal goat oocytes by slicing of ovaries from slaughtered animals while adult goat oocytes were collected by the laparoscopic ovum pick up (LOPU) method. Blastocysts were vitrified/warmed using the cryotop technique. Survival rates were determined in terms of blastocoele re-expansion at 3 and 20 h post-warming. For prepubertal goats, survival rates at 3h post-warming were significantly higher when expanded blastocysts (78.3%) were vitrified/warmed compared to hatched blastocysts (57.4%), whereas non-expanded (62.5%) or hatching blastocysts (71.4%) showed similar rates. For adult goats, survival rates were significantly higher after warming in expanded (36.4%), hatching (75%) or hatched (50%) blastocysts when compared to non-expanded (0%) blastocysts. When survival rates were assessed at 20 h post-warming, no differences were observed when we compared non-expanded (45.8%), expanded (56.5%), hatching (64.3%) and hatched (50.5%) blastocysts from prepubertal goats; and for blastocysts from adult goats, survival rates were only significantly lower for the non-expanded stage (0%) compared to the other stages. For adult versus prepubertal blastocysts at the same developmental stage, our data indicate significantly higher survival rates at 3 h post-warming for non-expanded and expanded blastocysts from prepubertal goats over their counterparts from adult goats. At 20 h post warming, survival rates were only higher for non-expanded blastocysts from prepubertal goats versus adult goats. Collectively, our data reveal that blastocysts produced in vitro from prepubertal goats return similar survival rates regardless of their development stage, whereas blastocysts derived from adult goats are best for vitrification at the expanded, hatching or hatched stage.