Cervical transfer of deep frozen cattle embryos

Abstract

Cattle blastocysts were collected from 29 donors 7–8 days after estrus and frozen and stored in liquid nitrogen up to several months. Two procedures were used for freezing and thawing: • - procedure A: slow cooling to −60°C (0.3C/min to −60°C) and slow thawing (12°C/min); • - procedure B: slow cooling to −30°C (0.3°C/min to −30°C) and rapid thawing in a water bath at 37°C. After thawing, the embryos were cultured from 8 to 12 hours before transfer; 36% of the embryos continued normal development during culture; both procedures resulted in a high pregnancy rate (procedure A: 10 15 ; procedure B: 11 15 ) after single cervical transfer of the frozen thawed embryos which developed normaly in vitro . However the overall survival rate was low (25%) and varied between donors, indicating that progress must be made before the technique of freezing can be extended to applied conditions.