It has long been implicated that transgenic cattle can be utilized as an animal bioreactor for the production of biomedical proteins because of their ability to synthesize and secrete an enormous quantity of milk proteins per head. In smaller animals such as sheep and goats, similar attempts have been successful, but not in cattle. This is largely due to the reproductive cycle of this animal species, namely long periods required for gestation and sexual maturity, and small number of calves obtained at a time. Besides the above, serious technical obstacles are the low efficiencies of in vitro embryo culture system, and transgene integration. Such characteristics make the production cost tremendously expensive. Moreover, with the current status of scientific progress, little is known about the way by which integrated transgene expression is enhanced. Should these obstacles be overcome, a new era may come in sight, in that each cow can become an animal bioreactor for supplying biomedical proteins demanded by the entire world for the year