Breeding for disease resistance--the prospective role of genetic manipulation

Economic considerations have meant that selection for resistance to disease has taken second place to that for productivity traits. Recent developments in genetic manipulation suggest that this may not be necessary in the future because it has become feasible to insert resistance genes into the genome of the fowl without compromising existing productivity traits. This review considers aspects of the genetic manipulation of disease resistance of the fowl, methods available for inserting genes and the identification of genes for insertion. It is concluded that of the technical strategies for inserting genes currently being developed those utilising defective, non-replicating retroviruses are the most promising. Studies to identify genes associated with resistance to disease are only now beginning. Although there has been some research into generalised immunological resistance to disease the results have been disappointing, and it seems likely that the use of specific resistance genes relating to each pathogen will be necessary. In particular the use of complementary or antisense genes to inhibit viral infections seems particularly promising.