Transgenesis in large domestic species: future development for milk modification.

The present review has two goals. First, to offer an overview of recent advances in the technical strategies applied to the production of transgenic large domestic animals, and second, to review how transgenic technology can be applied to the modification of milk composition. Transgenic sheep and cattle obtained through nuclear transfer are now a reality, opening up a means of ruminant transgenic production with an efficiency that entitles us to consider it a serious alternative to microinjection. Nuclear transfer also consistently reduces the time needed to establish a transgenic production herd, and what is more important, it opens up the way to homologous recombination in large species, which at the moment is restricted to mice. Other interesting technological contributions have also taken place lately, some of them towards the modification of the male germ line, and others developing viral vectors with the ability to alter the genetic information of animals. The simplification of the methodology and the consistent reduction of the time needed to carry out a transgenic experiment will allow us to test several hypotheses directed at the modification of milk components. This may help towards the application of transgenic technology in the dairy industry, which unlike pharmaceutical companies, has been somehow reluctant over these approaches.