For cattle producers and veterinarians, bovine respiratory disease complex (BRDC) presents a perplexing and persistent challenge. BRD is the most common disease and cause of death loss in cattle, and about 20 different pathogens can be involved in cases.  And in spite of constant advancements in vaccines, treatments and management practices intended to improve animal health, we’ve seen little improvement in BRDC prevalence, which accounts for losses of about $500 million annually in the United States.

In a presentation at the recent Beef Improvement Federation (BIF) conference, Washington State University animal scientist Holly Neibergs, PhD, noted that producers and researchers have long noticed variation in the apparent susceptibility to BRD between breeds or genetic lines of cattle, suggesting a genetic component to an animal’s susceptibility or resistance to the disease.

Researchers at multiple institutions currently are working to compile large volumes of phenotypic data related to BRD as part of a large collaborative USDA grant program. The project involves researchers at Texas A&M University, Washington State University, University of California-Davis New Mexico State University, Colorado State University, University of Missouri, USDA’s Agricultural Research Service and Gene Seek Inc. James Womack, PhD., Texas A&M University, is project director for the study.

One of the project’s goals is to identify regions of the genome related to BRD susceptibility and use those markers as proxies for the actual genes involved.

As part of the project, Neibergs and her team conducted a trial with 1,000 cattle in a large commercial Colorado feedyard. The goals of this study were to estimate the heritability of BRDC susceptibility in feedlot cattle at a commercial facility that did not treat cattle with meatphylaxis, estimate the rate of genetic change that would result from selection for cattle that were less susceptible to BRDC and determine the economic gain of selecting cattle for reduced BRDC susceptibility in the feedlot based on the estimated rate of genetic change.

The researchers co-mingled calves in feedyard pens, with half of the cattle in each pen diagnosed with BRD and the other half healthy controls. They collected samples for genomic profiling of each animal, along with treatment data and lung scores, and conducted an economic analysis of treatment and control groups.

The researchers calculated heritability of susceptibility or resistance to BRD using genotypes of each animal derived from the Illumina BovineHD gnomic assay. They used two different phenotype measurements of BRD to estimate heritabilities. The first phenotype was a binary case-control phenotype where cases had McGuirk health scores greater than 5 and controls had scores Less than 5 using a scoring system developed by University of Wisconsin veterinarian Sheila McGuirk.  The second BRDC phenotype used numerical values of the McGuirk system, ranging from 0 to 12, as a semi-quantitative phenotype. The heritability estimate for the case-control phenotype was 17.7 percent and for the clinical score phenotypes was 29.2 percent. These estimates were similar to those estimated

in previous studies.

The researchers estimated a potential annual rate of genetic gain through selection based on these at 1.2 using the case-control heritability estimate and 2.1 percent using the heritability estimate based on clinical scores. They estimated an economic cost of $204 per BRD feedlot steer based on loss of carcass quality, death and treatment costs. When this value was combined with the 16.2 percent national prevalence of BRDC in the feedlot and the estimated rate of genetic gain through selection, the researchers estimated the feedlot industry could gain between $8 and $16 million per year through the implementation of selection for cattle that are less susceptible to BRDC.

The Power Point slides, audio recording and proceedings paper from Neibergs’ presentation are available at the BIF Conference website