Microsurgical bisection of porcine morulae and blastocysts to produce monozygotic twin pregnancy.

Porcine morulae were bisected by a glass needle after softening of zonae pellucidae by pronase followed by a treatment with 0.05% trypsin/0.02% EDTA for decreasing intercellular junction of blastomeres. Transfer of 49 half-morulae to three recipients resulted in one pregnancy. The blastocysts were bisected symmetrically so as to leave a cellular bridge between the sister half-embryos after the softening of zonae followed by or without the trypsin/EDTA treatment. Transfer of 47 monozygotic (MZ) pairs of half-blastocysts to nine recipients resulted in four pregnancies. A litter of nine fetuses was obtained from seven MZ pairs of half-blastocysts, demonstrating that at least two pairs of MZ twin fetuses were produced. It is thought that the procedure for bisecting blastocysts developed in this study is one of the potential methods of producing porcine MZ twins.