Establishing value/utility of thyroid hormone response as a biomarker for prediction of the resilience of swine following PRRSV infection

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Porcine reproductive and respiratory syndrome (PRRS) is one of the most important diseases of pig production worldwide. Infection during pregnancy results in abortion and reduced litter size and quality, whereas infection after birth results in respiratory disease and immune suppression. Thus, the disease has a major impact on health, production, pig welfare and environmental footprint (more sows are required) in the Canadian pork industry. The PRRS virus evolves rapidly, similar to influenza virus, making vaccination less than 100% effective. Even vaccinated animals are prone to reinfection by different strains of virus. Producers can undertake costly procedures to eliminate the virus from their farms, but farms often become re-infected within 1-2 years. For these reasons, alternative methods of control are justified. The overarching objective of this research is to discover biomarkers measured in the blood that will predict resilience to PRRS. If genetically linked, it may be possible to select animals that have increased resilience to PRRS. Two biomarkers will be investigated using sera collected from past animal experiments conducted by researchers in Canada and the USA. Use of archived samples reduces the cost and increases the speed at which it can be completed. In Phase 1, sponsored by Ontario Pork, soluble CD163 will be measured in the serum of approximately 2,200 animals across various age groups. Soluble CD163 is a marker of inflammation and the requisite receptor used by PRRS virus to replicate in an animal's immune cells. In Phase 2, sponsored by NSERC, thyroxin hormone levels will be measured in the serum of approximately 4,650 pigs. These include the same samples as used for phase 1 plus additional cohorts to enable three genome wide association studies (GWAS). The thyroxin hormones have many functions related to regulation of appetite, metabolism, growth and fetal development. If either marker is heritable, our results will significantly improve the robustness of the Canadian swine herd, thereby improving industry competitiveness, productivity and welfare.**