Cryopreservation of Day 8 equine embryos after blastocyst micromanipulation and vitrification

Comparison of different cryopreservation methods for horse and donkey embryos

“…Fragmented nuclei without DNA fragmentation may represent the activation of another apoptotic pathway. Nevertheless, apoptosis seems to be one of the crucial mechanisms controlling the health of future offspring, although the precise threshold frequency of apoptosis that is detrimental has not been determined [5]. Some authors propose that apoptosis is a mechanism for the elimination nonfunctional, abnormal and misplaced cells from in vivo embryos [25].…”

“…It has been postulated [24] that the apoptotic index might not be a good indicator of embryo viability, since high apoptotic indices were detected in embryos with low dead cell rates and good morphological quality. Nevertheless, apoptosis seems to be one of the crucial mechanisms controlling the health of future offspring, although the precise threshold frequency of apoptosis that is detrimental has not been determined [5]. On the other hand, the higher incidence of apoptotic cells in manipulated (cryopreserved or in vitro produced) embryos, in contrast to the absence of these cells in in vivo embryos, could be a reflection of the high impact of these procedures on the viability of embryos, as demonstrated by the lower pregnancy rates associated with this kind of manipulated embryo.…”

“…However, their small size means that uterine recovery is a more labour intensive task. Although embryos >300 lm are relatively easy to recover, they are accompanied by additional impediments to survival after cryopreservation (the presence of a capsule makes them less permeable to the cryoprotectants, the large blastocoel volume induces the formation of ice crystals and the expression of aquaporin channels in their membranes is also altered) [5]. Although embryos >300 lm are relatively easy to recover, they are accompanied by additional impediments to survival after cryopreservation (the presence of a capsule makes them less permeable to the cryoprotectants, the large blastocoel volume induces the formation of ice crystals and the expression of aquaporin channels in their membranes is also altered) [5].…”

“…Various options are available to evaluate the efficiency of embryo cryopreservation, such as morphological evaluation, assessment of cell and ultrastructural injuries using specific stains, in vitro culture after thawing or warming, assessment of post-thaw embryo metabolism and determination of biosynthesis, and/or viability after embryo transfer to recipients [3,5,9,10]. Many of the cryopreservation methods described above and a range of cryoprotectants have been tested in horses.…”

“…In addition, several factors such as the age of the mare, the season and the type of semen have a bearing on embryo growth [1], which may account for the high variability in embryo size at a given time after ovulation. Although embryos >300 lm are relatively easy to recover, they are accompanied by additional impediments to survival after cryopreservation (the presence of a capsule makes them less permeable to the cryoprotectants, the large blastocoel volume induces the formation of ice crystals and the expression of aquaporin channels in their membranes is also altered) [5]. Recent studies lend support to the contention that enhanced cryosurvival can be achieved in large embryos (>300 lm) through micromanipulation and aspiration of blastocoel fluid prior to exposure to vitrification solutions [5,6].…”