Pregnancy rates with bisected bovine embryos.

A method for producing identical twin calves is described in which 5.5 to 7.5 day bovine embryos were bisected using a fine microsurgical blade. The resulting demi-embryos were transferred surgically or nonsurgically to the uterine horn ipsilateral to the corpus luteum of synchronous recipients (+/- 2 days), one demi-embryo per recipient. The mean pregnancy rate per demi-embryo was 48% (157/330), and per whole embryo split, it was 95% (157/165). Pregnancy rate was dependent on the stage of embryonic development. The pregnancy rate from bisected early morulae, 16% (7/44), was lower than that from bisected early blastocysts, 60% (58/96) P<0.01. The rate of identical twin production per embryo split reflected these pregnancy rates. Bisected blastocysts resulted in more identical twin sets, 39% (24/62), than early morulae, 9% (2/22) P<0.01. When used with normal embryo transfer procedures, this technique provides a method for routine production of identical twin calves. Furthermore, more calves are produced per two demi-embryos than per whole embryo.