- Genetic resistance to disease is the inherited ability of an animal to resist infection, limit pathogen multiplication, or reduce the severity of disease after exposure. It is an important trait in livestock and other animal breeding populations because it can improve animal health, welfare, productivity, and the sustainability of breeding systems. Genetic resistance varies among individuals and breeds because animals inherit different genetic variants that influence immune function, physiological responses, and interactions with pathogens.
- Disease resistance is influenced by multiple genes as well as environmental conditions, nutrition, management, vaccination, and pathogen exposure. Some resistance traits are controlled by major genes with relatively large effects, while many others are polygenic traits influenced by numerous genes, each contributing a small effect. The major histocompatibility complex (MHC), immune-related genes, and genes involved in pathogen recognition and inflammatory responses can influence resistance to particular diseases. However, the genetic mechanisms differ among pathogens and animal species, so a variant associated with resistance in one population may not have the same effect in another.
- Genetic resistance should be distinguished from disease tolerance. Resistance reduces the ability of a pathogen to establish, multiply, or persist in the host, whereas tolerance allows an animal to maintain health or performance despite a given level of infection or pathogen burden. Both characteristics can be valuable in breeding programs, but they have different biological effects. Selection for resistance may reduce infection or pathogen transmission in some circumstances, while selection for tolerance can improve animal welfare and productivity without necessarily reducing the spread of infection.
- Breeders can evaluate genetic resistance using disease records, clinical observations, laboratory tests, pathogen measurements, and information about the exposure of individual animals. Reliable assessment requires distinguishing genetic differences from environmental influences, because animals that appear disease-free may simply have experienced less exposure. Heritability estimates, genetic correlations, and estimated breeding values help determine whether resistance can be improved through selection and how it relates to other traits. Genomic data can also support the estimation of genomic breeding values, particularly when resistance is difficult or expensive to measure directly.
- Genomic selection and conventional selective breeding can be used to improve disease resistance over generations. In some cases, validated DNA tests identify specific variants associated with resistance or susceptibility, allowing breeders to incorporate this information into mating and selection decisions. For complex diseases, however, selection based on genomic predictions and well-recorded health traits is often more useful than relying on a single genetic marker. Breeding objectives should also consider genetic diversity, because intensive selection on a small number of resistance-associated variants may increase relatedness or reduce variation needed to respond to future pathogens.
- Genetic resistance can have trade-offs with other economically important traits. For example, resistance may be genetically correlated with growth, milk production, fertility, immune activity, or other health characteristics. These relationships are not universal and must be evaluated in the relevant population. A balanced selection index can combine disease resistance with production, reproductive performance, longevity, and welfare traits to avoid excessive emphasis on a single characteristic. Breeders should also monitor disease outcomes and genetic trends to confirm that selection produces meaningful improvements under practical conditions.
- Genetic resistance is not a substitute for vaccination, veterinary treatment, biosecurity, appropriate nutrition, or good animal management. Instead, it provides an additional long-term strategy for reducing disease burden and improving population resilience. By combining accurate disease recording, genetic evaluation, genomic tools, and balanced breeding objectives, animal breeders can develop populations that are better equipped to withstand disease challenges while maintaining productivity, welfare, and genetic diversity.
