Abstract
In Experiment I, a suitable combination of a vitrification solution (VS) and a rehydration solution (RS) was investigated for efficient cryopreservation of in vitro fertilized (IVF) bovine blastocysts on day 7. The variable of the VS is the concentration of polyvinylpyrrolidone (PVP) and that of the RS is the concentration of trehalose. Embryo development of 79% and hatching of 73% were obtained with VS4, 40% ethylene glycol (EG) + 11.3% trehalose + 12% PVP and RS1, 0% trehalose combination. In Experiment II, IVF bovine embryos on days 7, 8 and 9 were vitrified in VS4 and rehydrated in RS1. The highest proportions of embryos reexpanded (84%) and hatched (68%) during culture when the age was day 7. In Experiment III, day 7 embryos which had been vitrified in VS4 and warmed in 30 C waterbath were kept in situ inside the straw at 5 C or 20 C for 5 min before rehydration in RS1. Significantly higher proportions of embryos developed in culture when they were kept at 5 C than at 20 C. Furthermore, 3 out of 5 recipients in which vitrified embryos had been directly transferred gave birth to normal calves. Therefore, day 7 IVF bovine blastocysts can be successfully vitrified in VS4 and can be directly transferred into an isotonic environment.
