Abstract
Bovine morulae, collected from the superovulated heifers 6 days after the estrus, were bisected with a fine glass blade. After the bisection, the monozygotic pairs were either cultured or trans-ferred nonsurgically to recipient heifers. In Group A, one half of the demi-embryos was encased in its own zona pellucida while the other half was left naked. In Group B, both halves were cultured or transferred without zona-pellucida. Six out of 16 demi-embryos (8 monozygotic pairs) in Group A and 7 out of 28 (14 pairs) in Group B developed into normal blastocysts after culture in BMOC-3 for 40 to 46 h. However, there was only one monozygotic pair of normal blastocysts in each of the groups. Twenty-eight demi-embryos (14 pairs) were transferred to 28 recipient animals in Group A, and 4 normal calves, including one pair of monozygotic twin were obtained. In Group B, 3 normal calves were born after the transfer of 16 demi-embryos (8 pairs), but there was no monozygotic twin. These data indicate that the zona pellucida is not absolutely necessary for the normal development of demi-embryo produced from the morula.
