Fig. 1.

Schematic representation of the transgenic production process. The coding region of the protein to be expressed is linked to mammary gland specific regulatory elements. The resulting transgene is introduced by pronuclear microinjection into embryos of the selected species (alternatively, somatic cell nuclear transfer using cell lines transfected with the transgene can be used as method to create transgenic sheeps, goats or cattle). Embryos are then transferred to the oviduct (or the uterus) of a surrogate mother and carried to term. Transgenic offspring are identified and, when mature, are either bred or hormonally induced to lactate. Expression level of the target protein in the milk of transgenic animals is determined and a suitable founder line is chosen for the generation of the production herd.