Viability of bovine blastocysts obtained after 7, 8 or 9 days of culture in vitro following vitrification and one-step rehydration.

This study examined morphological appearance, viability and hatching rates in relation to the total cell number following vitrification of in vitro produced bovine blastocysts and expanded blastocysts. In Experiment 1, embryos obtained after 7, 8 or 9 d of culture were pooled and equilibrated in either 10% ethylene glycol (EG) or 10% EG plus 0.3M trehalose in Dulbecco's phosphate buffered saline (DPBS) supplemented with 10% calf serum and 0.6% BSA for 5 min each, at room temperature, and then vitrified together in precooled vitrification solutions consisting of 40% EG (Treatment 1), 40% EG plus 0.3M trehalose (Treatment 2), 40% EG plus 0.3M trehalose and 20% polyvinylpyrrolidone (PVP, Treatment 3) in DPBS. The embryo viability and hatching rates of Treatment 1 (19 and 3%) differed significantly (P < 0.05) from those of Treatment 2 (56 and 31%) and Treatment 3 (70 and 43%). There was a significant difference (P < 0.05) in embryo viability between Treatment 2 (31%) and Treatment 3 (43%). In Experiment 2, Day 7, 8 and 9 embryos were vitrified separately, with higher viability and hatching rates in Experiment 1 than in Experiment 2. The viabilities of Day 7 (87%), 8 (71%) and 9 (46%) embryos differed significantly (P < 0.05). Again, there were significant differences (P < 0.01) among the hatching rates of Day 7 (75%), 8 (38%) and 9 (9%) embryos. The total cell number of hatched blastocysts was then determined by differential fluorochrome staining. The total cell number of Day 7, 8 and 9 embryos differed significantly (P < 0.05).