The USDA estimated 78% of US beef operations and 89% of US dairy operations are seropositive for Bovine Leukemia Virus (BLV). Cattle infected with BLV may suffer reduced immune function and productivity. Animals with advanced BLV infections may develop lymphoma, leading to carcass condemnation at slaughter. Research has revealed growing evidence of host genetic markers associated with BLV infection. While research on BLV in beef cattle is limited, BLV research in dairy cattle is plentiful. In dairy cattle, evidence of an association between the Bovine Leukocyte Antigen (BoLA)-DRB3 gene locus and proviral load (PVL) has been reported. However, these associations have not been explored in beef cattle. Chapter 1 investigates associations between BoLA-DRB3 alleles and BLV PVL in upper Midwest beef cattle populations (n=157). Associations between BLV PVL and BoLA-DRB3 alleles was determined. Alleles DRB3*033:01 and DRB3*002:01 were found to be associated with lower PVL and DRB3*026:01 with higher PVL. Chapter 2 explores epigenetic relationships between dam and her calf. Epigenetics can be studied through microRNAs (miRNA), a small noncoding RNA species involved in post-transcriptional gene regulation. Variations in maternal environment have long been associated with fetal development and health. The study will measure differential expression of circulating miRNAs in calves born to BLV infected dams (n=24). The study found four miRNAs in 14-day old calves born to BLV infected dams. Literature indicates the miRNAs are associated with immunological response, skeletal muscle development, and cardiac development. The presented thesis provides some of the first insights of allelic and epigenetic regulations associated with BLV infections in cattle.
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