Improvement of survival rate of frozen cattle blastocysts after transfer with trophoblastic vesicles.

An experiment was conducted to determine if the loss of viability due to deep freezing could be overcome by addition of trophoblastic tissue to the embryo at transfer time. Forty-nine recipient heifers in a cotransfer group each received one frozen blastocyst + two frozen trophoblastic vesicles. The confirmed pregnancy rates by Day 45, 60, and 90 were 73, 61, and 57%, respectively. In a control group of 53 recipients that received only a frozen blastocyst, pregnancy rates for the same periods were 43, 42, and 40%, respectively. The difference between groups was highly significant by Day 45. The addition of trophoblastic vesicles to frozen embryos contributed to luteal maintenance in recipients and likely magnified the intensity of embryonic signals resulting in improved pregnancy rates.