Bovine respiratory disease (BRD), also known as pneumonia or shipping fever, is the most costly disease in the U.S. cattle industry, particularly for the feedlot sector. More than 1 million animals are lost each year to BRD, at an estimated price tag of more than $1 billion.

There’s hope on the horizon for prevention of BRD, however. Today’s genetic selection tools are allowing researchers to investigate — and hopefully find — genetic approaches to select for cattle less susceptible to this disease complex.

In fact, several research groups are working together on the Bovine Respiratory Disease Complex (BRDC) Coordinated Agricultural Project (CAP). These CAPs are awarded USDA grants to promote collaboration, communication and the exchange of information among individuals, institutions, states and regions. The BRDC project involves researchers at Texas A&M University (TAMU); Washington State University (WSU); University of California, Davis (UC Davis); New Mexico State University, (NMSU);  Colorado State University (CSU); University of Missouri (MU); USDA’s Agricultural Research Service; and Gene Seek Inc. of Lincoln, NE.

A five-year project

Now in its third year, this five-year CAP began by looking at 2,000 dairy calves (half as BRD cases and half as controls), and 2,000 feedlot animals (BRD cases and controls), to determine if genetic differences exist — genotyping them with a high-density single-nucleotide polymorphism (SNP) chip. The next step is validating the findings by using genotypes from an additional 1,000 dairy and 1,000 beef case/control animals from different geographic locations. It’s hoped the research leads to genetic tests to identify animals either resistant or susceptible to BRD.

TAMU’s Jim Womack is project director. He says CAP grants require a three-pronged approach of research, education and utilization of Extension networks to integrate producers, industry, veterinarians and researchers. Alison Van Eenennaam, UC Davis, leads the Extension component, while WSU’s Holly Neibergs heads the research component. CSU’s Milt Thomas (formerly at NMSU) and Robert Hagevoort at NMSU head the education component.

“The science being done here in Texas is mainly data analysis,” says Womack, whose group oversees the project. Most of the animals for the study were collected in California, Colorado and New Mexico.

Neibergs says multiple projects are progressing simultaneously. “I try to keep everyone in the loop as we figure out which things work and which things don’t, and all the adjustments,” she adds.

Genetic differences

Blood samples are taken for genotyping, along with diagnostic swabs from nasal passages. The blood samples are processed at WSU, while diagnostic samples are split and sent to labs at UC Davis or WSU.

“From the blood, we extract DNA and keep the white blood cells in long-term storage. We split all samples and have backup samples at MU in case something happens to one of our facilities. We have data for each sample, such as the animal’s identification, age and diagnostics,” Neibergs says.

The DNA is extracted and sent for genotyping to GeneSeek®. “GeneSeek provides us with genotype data on 780,000 genetic variants for each animal. For 6,000 animals, times 780,000, this is a lot of variants. We conduct genetic analysis of those genotypes at WSU,” she adds.

MU’s Jerry Taylor and TAMU’s Christopher Seabury also analyze the samples, but use a slightly different approach. “If we get the same results, we’re more confident in our identification of the genomic regions associated with susceptibility to BRD,” Neibergs explains.

The first set of nearly 3,000 dairy cattle has been completed, while the beef side is well underway, utilizing a feedyard in Colorado, she adds.

“We’ll end up with 2,000 feedlot samples and another 1,000 samples from a Grow-Safe system, which allows measurement of individual feed intake. We’ll have individual data on all the animals that get sick, and those that don’t. We can compare differences in weight gained between the sick and healthy animals, treatment costs — and how many didn’t recover.”

Neibergs says these data will provide a good estimate on BRD’s actual cost to a feedlot operation, and how illness affects animals’ ultimate performance. The cattle will be followed through the processing plant to assess how BRD affects carcass weight, yield and quality. Economic losses through the feedlot and processing will be calculated.

“This will tell us how much a producer can invest to prevent BRD, and what premiums could be passed to cow-calf producers and stocker operations to have BRD-resistant cattle,” Neibergs says. 

But breeding for animals less susceptible to BRD is just one component of preventing BRD. Animal selection must be done in conjunction with best management practices, Neibergs adds. Economic analyses will determine the breakeven spending limit on breeding, health and preconditioning programs.

Womack’s team at TAMU is looking at copy number variation in the genes. “We’re looking at one particular type of variation that occurs in genomes. These are called SNPs. Another type of variation more recently discovered is the copy number variations [CNVs],” Womack says.

The heart and soul of this project is the SNP assay, looking at the big SNP chips with thousands of variants over several thousand cattle, Taylor says.

“The smaller part is being done here, looking at CNVs. We’re screening the whole genome to find the important differences between animals that get sick and animals that don’t.” Eventually, he says, this will lead to discovery of the genes responsible. And that could lead to genetic tests aiding in selection, new vaccines, new diagnostics, new treatments, etc., to reduce BRD.