- Genetic susceptibility to disease is the inherited tendency of an animal to be more likely to develop a particular disease, experience more severe symptoms, or respond less effectively to an infectious agent or other health challenge. It is an important concept in animal breeding because genetic differences influence disease risk, health, productivity, reproductive performance, and animal welfare. Understanding genetic susceptibility helps breeders identify animals with increased inherited risk and develop breeding strategies that improve disease resilience across generations.
- Genetic susceptibility can result from variations in genes involved in immune function, pathogen recognition, inflammation, tissue structure, metabolism, and physiological regulation. Some disease-associated variants have relatively large effects, while many susceptibility traits are polygenic, meaning they are influenced by numerous genes with small individual effects. The major histocompatibility complex (MHC) and other immune-related genes can influence susceptibility to particular infections, although their effects depend on the pathogen, animal species, breed, and environment. A genetic variant associated with disease risk in one population may not have the same effect in another.
- Disease susceptibility is not determined by genetics alone. Environmental conditions, nutrition, housing, hygiene, vaccination, pathogen exposure, age, and management practices can all influence whether a susceptible animal develops disease. Genotype–environment interaction occurs when genetic differences affect performance or disease outcomes differently under different conditions. Consequently, animals should be evaluated under appropriate and comparable conditions whenever possible. An animal that remains healthy may have greater genetic resistance, but it may also have experienced less exposure or benefited from better management.
- In quantitative genetics, disease susceptibility can be evaluated using health records, clinical diagnoses, laboratory results, pathogen measurements, and information about disease exposure. Heritability estimates help indicate how much of the observed variation in a trait is attributable to genetic differences within a particular population and environment. Genetic correlations reveal whether susceptibility is associated with other traits, such as growth, fertility, milk production, survival, or immune function. These relationships are important because selection for high production without considering health may produce undesirable correlated changes in some breeding populations.
- Genetic testing and genomic selection can support the identification of inherited disease risks. When a well-characterized variant is associated with a particular disorder, a DNA test may help identify animals carrying that variant. For complex diseases influenced by many genes, genomic evaluations and estimated breeding values can be more useful than relying on a single marker. However, a genetic association does not always prove causation, and a susceptibility-associated variant does not necessarily mean that an animal will develop the disease. Genetic results should be interpreted alongside clinical evidence, pedigree information, and population-specific research.
- Breeding programs can reduce genetic susceptibility by selecting animals with more favorable health outcomes and breeding values, while maintaining genetic diversity and balancing other breeding objectives. Selection should consider disease resistance, survival, fertility, productivity, welfare, and adaptation rather than focusing exclusively on one trait. Excessive reliance on a small number of breeding animals can increase inbreeding and reduce the genetic variation needed to respond to emerging diseases. Regular monitoring of disease frequency, genetic trends, and population relatedness helps breeders evaluate progress and identify potential risks.
- Genetic susceptibility should also be distinguished from genetic resistance and disease tolerance. Resistance generally refers to an animal’s ability to limit infection or pathogen multiplication, whereas tolerance describes its ability to maintain health or performance despite infection or pathogen burden. Susceptibility refers to an increased tendency to develop disease or experience adverse outcomes. These traits can overlap, but they represent different biological processes and may require different selection strategies.
- Managing genetic susceptibility is most effective when integrated with vaccination, veterinary care, biosecurity, appropriate nutrition, and good animal management. Genetics can reduce inherited risk over generations, but it cannot eliminate every disease or replace effective prevention and treatment. By combining reliable disease records, genetic evaluation, genomic tools, and balanced selection objectives, animal breeders can reduce disease burden, improve animal welfare, and develop healthier, more resilient breeding populations.
