Genetic engineering of laboratory and livestock mammals.

Recent advances in recombinant genetics have made possible the transfer of cloned genes from one organism to the genome of another. Research with mice made transgenic by insertion of rat or human genes has provided direct evidence that transferred genes can be incorporated into the germline and expressed in the recipient. Current technology for gene transfer involves microinjection of the recombinant genes into the male pronucleus of the zygote. Resulting transgenic mice, when mated as adults, produced offspring that contained and expressed the transgenes. These observations serve as indications of the possibilities that exist for genetic engineering in livestock species. Although there are some technical problems to be overcome before livestock embryos can be genetically altered by these means, the genes for producing growth hormone transgenic livestock are currently available, and research groups are working toward this objective. In addition to this work with growth hormone genes, there are many other potential applications for genetic engineering livestock to produce more highly efficient production; however, there is considerable research to be done before the full potential of this technology can be achieved. It will be necessary to identify other genes that have potential for improving the production efficiency of livestock, and it will be necessary to gain a more complete understanding of the developmental and molecular biology of livestock. The potential impact of this technology in farm animal production is enormous, but, in the short term, it will be a costly endeavor.