ABSTRACT
Pronuclear microinjection of bovine zygotes is currently the method of choice for the production of transgenic cattle. In principle, two major systems for the generation of bovine embryos can be discriminated. One is based on the use of zygotes, recovered from the oviduct of donor cows via surgery or slaughter after superovulation and artificial insemination. The other system is based on the in vitro generation of zygotes, in which case oocytes are collected from slaughterhouse ovaries and are matured and fertilized in vitro. The capacity of bovine zygotes generated in vivo to develop to the morula/blastocyst stage is ca. 2-fold higher than that of embryos generated in vitro. Some of the advantages of the superovulation and the in vitro embryo generation protocols can be combined by the use of transvaginal ultrasound-guided oocyte recovery from live donors. Donor animals, Holstein-Friesian heifers, were screened for health status before they were transported to the farm.
