Genome-wide association study of bovine respiratory disease complex in U.S. feedlot cattle

Abstract Text: Bovine respiratory disease complex (BRDC) is the leading natural cause of morbidity and mortality among feedlot cattle, and is responsible for substantial economic losses during commercial beef production. The primary objective of the present study was to estimate the heritability of two related BRDC traits in U.S. feedlot cattle (binary case-control; clinical severity scores), and identify quantitative trait loci (QTL) associated with differential susceptibility to BRDC. All beef cattle (Angus, Red Angus, Taurine Crossbreds, Charolais, Hereford) were sampled from commercial feedlots in Colorado (CO) and Washington (WA), with BRDC phenotypes assigned using the McGuirk diagnostic scoring system.  Similar numbers of heifers (928) and steers (934) were genotyped using the Illumina BovineHD BeadChip, which included 932 BRDC cases, and 930 controls. Genome-wide association analyses were performed using a linear mixed model (EMMAX) with genomic relationship matrix (G), and accounted for the effects of month, season, breed, lot-pen, days-to-pull, sex, year sampled, and location in the combined cohort (CO+WA).  Heritability estimates for the BRDC binary case-control and clinical score phenotypes ranged from 0.13-0.14 in CO, 0.25-0.20 in WA, and 0.20-0.22 in the combined cohort, respectively; thereby suggesting that a common set of susceptibility loci were likely to exist. QTL estimated to explain ≥ 2% of the variance in either of the BRDC phenotypes were detected in each individual population (CO, WA), whereas the most significant QTL detected for the combined cohort were estimated to explain ≥ 1% of the variance in both BRDC phenotypes. The genomic positions of several binary and clinical scores BRDC QTL were found to overlap in all analyses (i.e., CO, WA, CO+WA); with the combined cohort producing overlapping QTL intervals (i.e., binary, clinical scores) on BTA1, BTA5, BTA8, BTA10, BTA13, and BTA27 thereby suggesting that genomic selection for reduced BRDC susceptibility in beef feedlot cattle is likely to help mitigate economic and production losses. This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2011-68004-30367 from the USDA National Institute of Food and Agriculture.

Keywords: Beef cattle, bovine respiratory disease complex, genome-wide association study, genomic selection