New Perspectives from Two Large NIFA Funded Grants: An Overview of GWAS Results

Selection of cattle that are less susceptible to bovine respiratory disease complex (BRDC), and more efficient with respect to feed utilization, are the primary goals of two ongoing NIFA funded projects focusing on U.S. beef and dairy cattle.  Heritability estimates for BRDC susceptibility among preweaned Holstein calves at two locations (NM, CA) ranged from 0.13-0.32, and was dependent upon the animal disease phenotype evaluated (i.e., binary; clinical scores) as well as the parameterization of the mixed model (i.e., including diagnostic data).  The largest-effect QTL for BRDC susceptibility were not shared between the two study populations (NM, CA), which was unsurprising given observed differences in BRDC pathogens (i.e., frequency distributions) detected at each location.  Nevertheless, strong positional candidate genes for BRDC susceptibility were identified, and further supported by published biological precedents. Heritability estimates for common feed efficiency (i.e., residual feed intake-RFI, dry matter intake-DMI) and growth traits (average daily gain-ADG, mid-test metabolic weight-MMWT) in several U.S. beef cattle breeds (Angus, Hereford, SimAngus) ranged from 0.18 to 0.61 across all of the investigated traits, with individual ranges across breeds as follows: RFI = 0.20-0.49; DMI = 0.18-0.46; ADG = 0.21-0.37; MMWT = 0.47-0.61.  Collectively, moderate to large-effect QTL were detected for all investigated traits, with little overlap across breeds.  However, some positional candidate genes were found to be conserved across food-animal species for the investigated traits.  Comparative analyses using Illumina 778K and SNP50 genotypes for all traits indicated that the lower density approach failed to detect all moderate to large-effect QTL.