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Are We Closing In On A Genetic Clue For BRDC Heritability

By: Jaime Pullman

One of the most costly scourges to the beef business, bovine respiratory disease complex (BRDC), is currently under the microscope. BRDC is the leading cause of death in beef and dairy calves. Respiratory diseases cost over $250 per affected feedlot steer when treatment, reduced carcass quality, and death loss are considered. Two research studies nearing completion right now hope to recognize the best management practices both in the pasture and the feedlot, and to identify those animals that are genetically more susceptible to BRDC. In combination, that could reduce disease incidence, thereby saving money, using fewer antibiotics and improving animal health.

Dr. Russ Daly, the state public health veterinarian and extension veterinarian and professor at South Dakota State University, is part of a three-year summer pneumonia research project now entering its final year. The study aims to examine and identify risk factors significantly associated with summer pneumonia in calves.

“All of us on the research team, as well as most cow-calf veterinarians you talk to, would indicate that we can see problems with summer pneumonia in very well-vaccinated, well-managed herds as well as in herds that do not employ extensive vaccination programs,” Dr. Daly shares.

“It is frustrating for us, as well as the producers, to know that one year can present problems and the next year no problems will be present at all. A fact that is very apparent so far is that there is no one single ‘silver bullet’ that ranchers can implement to prevent summer calf pneumonia. If it was an easy question to answer, we likely would have found the answer by now!”

Dr. Daly recommends identifying management practices that ‘make sense’ first by working with their local veterinarian. What vaccines might be helpful? What issues are other producers in the area dealing with?

“We also want to look at potential sources for different strains of respiratory viruses or bacteria to come into a group of calves,” Dr. Daly continues. “Separation of young calves from feedlot animals, for example, would make sense. Knowing your herd’s risk for or status concerning BVD persistent infections also makes sense. A cow or calf persistently infected with BVD virus will spread a great amount of virus to their herd mates; BVD virus greatly suppresses the immune system.”

Disease shedding is no stranger to the feedlot, which is where another research project on the BRDC hunt is taking place. The Integrated Program for Reducing Bovine Respiratory Disease Complex in Beef and Dairy Cattle Coordinated Agricultural Project (BRDC CAP) is a 5-year USDAfunded project being conducted by six different universities led by Texas A&M University’s Dr. James Womack and USDA ARS.

The research examined both pre-weaned dairy heifers (Holstein) and beef feedlot steers (Bos Taurus). Using a health scoring system, the researchers identified BRDC cases and then applied genomic technology that allowed them to estimate heritability for BRDC susceptibility. The resulting susceptibility ranged from 19 to 21 percent in the dairy animals and up to 29.2 percent in the beef.

IT ALL ADDS UP OVER TIME

Researchers believe genetic change could reduce the BRDC incidence by one to two percent per year, which might not sound like much but would be substantial over time.

“When an economic analysis was conducted based on the differences in harvested value of BRDC affected steers, their treatment costs, and death losses,” explains Dr. Holly Neibergs, “it was estimated that the feedlot industry was losing over $1 billion annually from this disease.

Based on our heritability estimates, if feedlot cattle were selected based on susceptibility to BRDC, significant economic gains ($13-21 million annually) could be realized by the feedlot industry.”

Dr. Neibergs is a geneticist, an associate professor at Washington State University, and a member of the BRDC CAP team. She first became interested in researching the possibility of reducing BRDC via genetics eight years ago.

Like Dr. Daly, she recognized that good management wasn’t everything. “I was struck with how the dairy and beef industries have identified best management practices, have routinely vaccinated their cattle and have had access to improved treatments to reduce bovine respiratory disease, but yet the prevalence, morbidity and mortality is similar to what was experienced twenty years ago,” Dr. Neibergs recalls.

More than 20 different researchers of different disciplines are involved with the BRDC CAP. The program, now in its final year, followed 500 healthy and 500 BRDC beef cattle in two feedlot locations (Colorado and Washington). Scientists sampled cattle and followed them to harvest, tracked diagnostic data on found pathogens, treatment costs, yield and quality grades, weights and genetic information.

Preliminary results are based on data from the Colorado facility, since the Washington cattle weren’t complete at the time of this article. Those results show that both BRDC susceptibility loci and BRDC estimated heritability were similar in beef feedlot steers and the pre-weaned dairy calves. Dr. Neibergs says that the markers that have been identified with BRDC will be supplied to commercial genotyping companies once the research is complete.

The researchers will soon be providing the markers for dairy, since that part of the project was completed first and the incorporation of markers into genetic panels for beef cattle will follow soon.

HOPES TO MAKE SIGNIFICANT GAINS

By making the research available to breed associations and commercial genotyping companies, BRDC resistance could be incorporated into EPDs and selection indexes for producers to use.

“The heritability estimates for BRDC were better than we had predicted and improved further as we more narrowly defined BRDC,” Dr. Neibergs shares. “This provides strong evidence that by selecting for animals that are not susceptible to BRDC, we will be able to make significant gains in reducing the morbidity, mortality and economic losses associated with the disease.”

The BRDC CAP research suggests that regional differences might be in play with higher frequency of BRDC pathogens in some areas than in others, but Dr. Neibergs explains, “It isn’t clear if these frequencies change over time, or are the result of different vaccination programs, or different genetics of the cattle being exposed to the disease pathogens.

Therefore, it seems important to use a multi-pronged approach where best management practices, vaccination, careful observation to identify and pull sick animals, and the addition of selection for cattle that are less predisposed to disease will result in both short term and long term reduction in BRDC.” Saving time and money, and improving the life of beef cattle is a long-term goal for scientists and producers alike.

Advancements in management and genetic selection could make BRDC more of a nuisance than a curse. And the willingness to work with researchers helps make those advancements possible. “We would really like to recognize and thank all of those in the cattle industry that have made these studies possible,” concludes Dr. Neibergs. “Without the cooperation and collaboration of the beef feedlot and dairy calf facilities, we would not have been able to conduct these studies.”

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