IN-VITRO VIABILITY OF CRYOPRESERVED EQUINE EMBRYOS FOLLOWING DIFFERENT FREEZING PROTOCOLS

The main objective of this study was to evaluate two freezing protocol s and the effect of agar embedding on survival of day 6.5 equine embry os. A total of 133 embryos were used, in one group (n = 51), embryos w ere first embedded in agar before the freezing protocol was started. A freezing protocol to -30 degrees C or -33 degrees C was used before p lunging embryos into liquid nitrogen (LN(2)). The embryos were thawed in water at 37 degrees C, evaluated and placed in culture, After 24 h culture, the embryos were evaluated for their morphology and developme nt. No differences were observed between embryos plunged at -30 degree s or at -33 degrees C in LN(2). The analysis of the morphology and dev elopment after thawing showed that the diameter and developmental stag e at freezing correlated with embryo survival. Morula and early blasto cyst stages of development were associated with better quality after f reezing and thawing and had a better potential to survive after in vit ro culture (p < 0.05) compared to more advanced stages. The agar faile d to protect embryos from zona pellucida damage, but a tendency to pre vent rupture was observed in larger embedded embryos.