Animal disease model
The second area of transgenic application in agriculture is to develop lines of animals resistant to some specific damaging diseases. While the genes of interest may be expressed in the transgenic animals, so far there have been no projects that have progressed to the development of disease resistant animal lines. Prion diseases have had a major economic impact arid are a concern in the use of animal products for human use. This is particularly the case for BSE in cattle, and it is now almost certain that this has caused a new and terrible form of Creuzfeldt Jacob disease (CJD) in humans termed vCJD. Scrapie has been described in sheep for many years and, from the evidence of PrP knockouts in the mouse, removal of the PrP gene itself by gene knockout would be expected to produce animals resistant to prion diseases, without detrimental side effects.
Knockout of the Cftr gene in the sheep would be expected to produce a more accurate model of cystic fibrosis in humans due to similarities in lung physiology between sheep and humans. Furthermore sheep lungs are similar in size to those of humans thus enabling medical interventions delivering new drugs or therapy with the Cftr gene to be evaluated more realistically. There are of course major ethical issues which would have to be considered in generating potentially sick animals and these would have to be balanced alongside the practical benefits such a model could bring.