Genetic Improvement of Immune Response and Disease Resistance: Past Experience and a Vision for the Future

The immune system is composed of integrated, genetically and environmentally regulated sets of cells and molecules that control the response to external and internal stimuli, including pathogenic microorganisms. In terms of infectious organisms, the response of the host largely reflects the relationship or adaptation between the host and agent. This response is influenced through genotype by environment interactions, both at the individual and population level. It may be that disease is largely the product of incompatible gene by environmental interaction. It is therefore particularly relevant to understand host-pathogen relationships and adaptations under various stress and management conditions. Improved understanding of the biology and genetic relationships between the host and pathogen, particularly those that effect the immune system during periods of production stress, should facilitate implementation of non-traditional approaches to improve the health of intensively reared livestock. Genetic regulation of immune response and selection for disease resistance in livestock is well documented and should be considered as an economical and prophylactic approach to improve animal health (reviewed by Stear et al., 2001). Diverse approaches however