1995 Volume 41 Issue 4 Pages 361-366
Immature bovine oocytes were equilibrated with a mixture of 1.6 M 1, 2-propanediol and various concentrations of sucrose (0, 0.01, 0.05, 0.1, 0.2 or 0.3 M) by the three-step method. Subsequently, the oocytes were cooled from 0 C to -5.5 C at a rate of 1 C/min. They were seeded at -5.5 C, cooled at a rate of 0.3 C/min to -30 C and plunged into liquid nitrogen. After being thawed and having their cyroprotectants diluted by the three-step method, the oocyte survival rate was assessed by examination of morphology and development following in vitro maturation/in vitro fertilization and culture. The rate of development of morphologically normal oocytes and of development to the two-cell stage in immature oocytes frozen in the presence of 1, 2-propanediol containing 0.3 M sucrose were significantly lower (P<0.05) than those observed at lower concentrations of sucrose (0 to 0.2 M). Of the oocytes frozen in the presence of 1, 2-propanediol containing sucrose at concentrations less than 0.2 M, very few frozen-thawed oocytes (0 M, 1.7%; 0.01 M, 1.3%; 0.05 M, 1.6%; 0.1 M, 0.6%; 0.2 M, 2.2%) developed to the blastocyst stage. Five blastocysts derived from immature oocytes frozen in the presence of 1, 2-propanediol containing 0.2 M sucrose were transferred nonsurgically to three recipients. Consequently, one recipient was diagnosed as pregnant with a single fetus by an ultrasonographer after 60 days of estrus.
