Single-nucleotide polymorphisms associated with performance traits in beef cattle grazing endophyte-infected tall fescue

Tall fescue (Lolium arundinaceum Schreb.) is the most prevalent forage in the Midsouth United States due in part to the presence of the endophytic fungus Neotyphodium coenophialum. The fungus, while conferring hardiness to tall fescue, contributes to decreased production efficiency in cow-calf operations. A previous genome-wide association study was performed using the Illumina 50k bovine SNP chip. Twenty-four SNP were found to be associated (P < 0.05) with adjusted birth weight and adjusted 205-day weights of calves from 48 beef cows at Ames Plantation. The first objective was to validate each SNP by testing associations with several additional phenotypes. Custom Taqman genotyping assays (Applied Biosystems, Foster City, CA) were subsequently designed to genotype each SNP in beef cattle located at Tennessee Tech University (n = 654), to validate associations in a large, independent herd. The results yielded 15 associations that were significant (P < 0.05) with 6 phenotypes linked to those affected by fescue toxicosis. The second objective investigated the link between fescue toxicosis and the XK, Kell blood group complex subunit-related, member 4 (XKR4) gene. Serum prolactin concentrations were significant (P = 0.0002) for an intronic SNP within the gene, suggesting further investigation into the physiological function of the gene as well as providing a potential genetic marker for selection for cattle resistant to fescue toxicosis. The results of this study validate the majority of findings from the GWAS and provide effective initial steps towards utilizing genetic markers to improve the resistance to fescue toxicosis in cattle.