A simple method for bisecting horse embryos

Summary Late morulae and blastocysts were recovered non‐surgically on Days 6 to 8 after ovulation (Day 0) from Czech warm‐blood mares which had been inseminated with fresh or frozen stallion semen. Three morulae and three early blastocysts were bisected using a microblade attached to a simple bisection tool fixed to the objective of a phase contrast microscope. The 12 resulting demi‐embryos and 13 intact (non‐bisected) blastocysts were transferred surgically via flank laparotomy to recipient mares which had ovulated +1 to −3 days with respect to the embryo donor. Pregnancy was established in nine of the 13 mares (69 per cent) which received intact embryos and in tow of the six mares (33 per cent) which received demi‐morulae. However, none of the six mares which received demi‐blastocysts became pregnant.