Abstract
Summary. Twenty six of in vivo embryos were collected from 7 Holstein cows and 1 Japanese black cows by single or superovulated flushing. Thirty one of in vitro embryos were produced using in vitro fertilization techniques using Japanese black oocytes aspilated from ovaries obtained local slaughter house. These embryos were suspended in 1.8 M ethylene glycol (EG) supplemented with 10% superovulated cows serum (scs) at 25 C and held 10 min, then embryos were loaded into 0.25 ml plastic straws, placed into an alcohol bath freezer at 0°C, cooled from 0°C to -7°C at 1°C/min, seeded, held for 10 min, cooled at 0.3 C/min or 0.5°C/min to -30°C. Straws were then plunged and stored in liquid nitrogen. After a 20 day storage period in liquid nitrogen, the cryopreserved straws were placed in air for 6 sec and plunged into 30°C water bath for thawing and transfered immediately into syncronized recipients. The pregnancy rates of 0.3°C/min [90% (9/10)] were significantly higher (P<0.01) than those of 0.5 C/min [12.5% (2/16)] for cooling rates in vivo embryos. And the pregnancy rates of in vitro frozen embryos were 63% (12/19).
