Transgenic Cows, Proembryos, Fertilized oocytes, Microinjected Zygotes, Vitro Embryo Production, Lactoferrin, Bioreactors

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	Transgenic Cows - In most earlier attempts (in Canada) for the production of transgenic cows, embryos or fertilized oocytes produced in vivo were utilized. Fertilized oocytes or proembryos were surgically retrieved from superovulated and artificially inseminated cows. Microinjected zygotes were then transferred by surgery either directly into the oviduct of recipient cows or into temporary hosts like sheep or rabbits. In view of two surgical operations, this method is labour intensive and more expensive.
In 'The Netherland', recently (1991) a technique has been developed for in vitro embryo production. In this new procedure, oocytes obtained from the ovaries of slaughter house cows, were matured and fertilized in vitro. Their pronuclei were microinjected with a construct containing a bovine alpha-SI-casein promoter (bovine = ox) driving a cDNA encoding the antibacterial human iron binding protein, 'lactoferrin'. The embryos were cultured to morula/blastula stage and, then non-surgically transferred to recipient females. Two of the 19 calves born from 103 transferred zygotes were transgenic (one male and other female). This procedure may facilitate the use of cows as bioreactors at the commercial level.