A previous study identified an association between DRGA, a single nucleotide polymorphism (SNP) on chromosome 7, and a substantial improvement in fetal viability following PRRSV infection of pregnant dams. This region includes a gene associated with metabolism of a hormone-linked to growth and other processes. Levels of this hormone decrease in fetal and maternal serum following a PRRSV infection and is likely to have a negative impact on fetal growth and development leading to virus-induced fetal death. The goal of this project is to identify genes in the region of the DRGA SNP to determine if it is causally associated with PRRSV fetal viability. Additionally, the project aims to further investigate how the thyroid hormone system is disrupted following PRRSV infection.  These findings could facilitate the natural selection of PRRSV resilient fetuses.