The influence of polyvinylpyrrolidone on freezing of bovine IVF blastocysts following biopsy.

A study was conducted to develop a better freezing protocol for in vitro developed biopsied bovine blastocysts. Biopsied blastocysts were exposed to 1.8 M ethylene glycol (EG) + 0.05 M trehalose (T) and different concentration (5, 10, and 20%) of polyvinylpyrrolidone (PVP). Exposure to the solutions alone did not affect their in vitro development (Experiment 1). Experiments 2, 3, and 4 tested the viability of biopsied blastocysts cryopreserved in 1.8 M EG + different concentrations of T (0, 0.05, 0.1, and 0.3 M), 1.8 M EG + different concentrations of PVP (0, 5, 10, and 20%), and 1.8 M EG + 0.05 M T + different concentrations of PVP (0, 5, 10, and 20%), respectively. The proportion of biopsied blastocysts that reexpanded following cryopreservation in 1.8 M EG + 0.05 M T (38.5%) and 1.8 M EG + 0.1 M T (36.1%) was significantly (P < 0.05) higher than the proportion that reexpanded in 1.8 M EG + 0.3 M T (13.9%) (Experiment 2). The viability and the percentage of embryos that developed to > 250 microns in diameter in the 5, 10, and 20% PVP groups (77.8 and 50.0%, 78.1 and 43.8%, 76.9 and 65.4%, respectively) were significantly higher than those that developed cryopreserved without PVP (55.1 and 20.7%) (Experiment 3). Optimum development of in vitro culture of frozen-thawed biopsied blastocysts was obtained using 1.8 M EG + 0.05 M T and 20% PVP. Analysis of blastocysts > 250 microns in diameter showed that the number of ICM cells of biopsied blastocysts cryopreserved in 1.8 M EG + 0.05 M T with or without PVP was not different from the number of unfrozen biopsied blastocysts. These results indicate that PVP has some beneficial effect on freezing of biopsied bovine blastocysts.