Molecular genetic manipulation can now be used to produce pharmaceutical proteins in the milk of farm animals. In the longer term this technology will be used to modify aspects of animal production, but it is not clear how many manipulations will be useful nor when such applications will become practicable. Improvements are required in all four aspects of an effective scheme for either gene transfer or targeting: it must be possible 1). to make the change, 2). to regulate expression of the gene in the desired manner, 3). to identify genes that are able to have a significant effect and 4). to disseminate the change into the target population.
There is only one method that has been used to transfer a gene in livestock and this depends upon injection of a few hundred copies of the gene into a nucleus in the early embryo. It is believed that integration occurs because the act of injecting fluid causes breakages in chromosomes and that the repair mechanisms sometimes include injected DNA. There are serious implications.