The techniques that are used to generate transgenic livestock are inefficient and expensive.  This, coupled with the fact that most agriculturally relevant traits are complex and controlled by more than one gene, has restricted the use of transgenic technology.  New methods for modifying the genome will underpin a resurgence of research using transgenic livestock.  This will not only increase our understanding of basic biology in commercial species, but might also lead to the generation of animals that are more resistant to infectious disease.