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This stduy was carried out in order to investigate the effects of concentration and equilibration time of cryoprotective agents on survival rate of slow and ultrarapidly frozen in vitro fertilized bovine embryos. In vitro fertilized bovine embryos, following dehydration by cryoprotective agents and sucrose, were slowly freezed(from 20^{circ}C to -7^{circ}C/-1^{circ}C/min., from -7^{circ}C -35^{circ}C/-0.2^{circ}C/min. from -35^{circ}C to -38^{circ}C/-0.3^{circ}C/min.) by cell freezer and directly plunged into liquid nitrogen and thawed in 38^{circ}C water. Survival rate was defined by development rate to the morula and blastocyst stage after in vitro cultured and FDA test. The results are summarized as follows : 1. The survival rates of in vitro fertilized bovine embryos after slow frozen-thawing in the freezing medium of 0.25M sucrose added 2.5M glycerol, 3.0M DMSO, 2.0M propanediol and 2.5M glycerol＋2.0M propanediol were 84.3%, 85.9%, 77.8%, 74.3%, respectively. 2. The survival rates of in vitro fertilized bovine embryos after slow frozen-thawing in the freezing of 0.50M sucrose added 2.5M glycerol, 3.0M DMSO, 2.0M propanediol and 2.5M glycerol＋2.0M propanediol were 83.8%, 85.1%, 71.4%, 74.6%, respectively. 3. The survival rates of in vitro fertilized bovine embryos after ultrarapid frozen-thawing in the freezing of 0.25M sucrose added 2.5M glycerol, 3.0M DMSO, 2.0M propanediol and 2.5M glycerol＋3.0M propanediol were 69.3%, 70.8%, 63.2%, 67.1%, respectively. 4. The survival rates of in vitro fertilized bovine embryos after ultrarapid frozen-thawing in the freezing of 0.25M sucrose added 2.5M glycerol, 3.0M DMSO, 2.0M propanediol and 2.5M glycerol＋2.0M propanediol were 69.4%, 70.1%, 62.3%, 63.5%, respectively. 5. The survival rates of in vitro fertilized bovine embryos after slow and ultrarapid fromthawing in the freezing medium of sucrose added cryoprotective agents were not significant difference between 5min. and 10min. of equilibration time.
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