We hear bovine respiratory disease (BRD) fittingly referred to as a “syndrome” (BRDS) or as a “complex” (BRDC) due to its multi-factorial nature. But in terms of its prevention and control, we can describe it as the bovine respiratory disease dilemma (BRDD?).

BRD is the most common, most damaging and most thoroughly researched disease in beef cattle. All that research has yielded more effective vaccines targeted to the pathogens involved in BRD, advanced diagnostic tools, fast-acting antimicrobials for efficacious treatment and adjustments in management philosophies to focus on prevention. In spite of these efforts though, we’ve seen little reduction in BRD incidence, and in fact, BRD morbidity rates have continued to increase in some settings.

BRD trends

In late July, veterinarians, researchers and producers gathered in Denver for the 2014 BRD Symposium, focused on the theme of “New Approaches to Bovine Respiratory Disease Prevention, Management and Diagnosis.” Purdue University veterinarian Mark Hilton, DVM, ABVP, kicked off the program with an overview of the past, present and future of BRD control in cattle. 

Hilton, and others throughout the conference, pointed out that in spite of advancements, BRD remains the number-one disease of stocker, backgrounder and feedlot cattle in North America. In feedlots in the United States, BRD accounts for 70 to 80 percent of all feedlot morbidity and 40 to 50 percent of all mortality. According to a 2011 feedlot study from the USDA’s National Animal Health Monitoring System (NAHMS), 16.2 percent of all feedlot cattle were treated for BRD.

In fact, Hilton says, we have a higher incidence of BRD in feedlots today than we had 20 years ago. According to NAHMS, data from 1994, 1999 and 2011 show BRD deaths increased from 10.3 per thousand head in 1994 to 14.2 per thousand head in 1999 and to 16, or 1.6 percent death loss by 2011.

The industry can do better, Hilton says, but there is no single, simple solution. Reducing BRD losses will require efforts across the production chain, with prevention measures beginning at the cow-calf stage.

Control of BRD is confounded by the multi-factorial nature of the disease complex. Viral pathogens involved can include Infectious Bovine Rhinotracheitis (IBR), Bovine Viral Diarrhea (BVD), Parainfluenza 3 (PI3), and Bovine Respiratory Syncytial virus (BRSV), while bacteria include Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis.

In addition to the pathogens, risk factors for BRD include stresses associated with weaning, surgical procedures at or near weaning, lack of immunity, changes in diet, comingling of cattle, transportation, dust, parasitism, concurrent diseases, and weather extremes.

During the BRDS symposium, Mike Engler, PhD, CEO, president and chairman of the board at Cactus Feeders, presented data showing BRD trends in Cactus feedyards over the past 13 years. With the company marketing nearly 1 million cattle per year, the dataset includes huge numbers and shows some clear trends relating to placement patterns and environmental effects on BRD incidence.

Engler says mortality during the finishing phase in beef steers has increased over the last 13 years at a rate of 0.05 percent per year for cattle fed in Cactus Feeders’ operations. During that time, the company shifted its emphasis toward placing heavier cattle than in previous years, which has corresponded with lower morbidity rates but higher case fatality rates.

Regression analysis of Cactus data indicates that mortality is increasing at an annual rate of 0.10 percent in 600 pound cattle, 0.06 percent in 700-pound cattle and 0.04 percent in 800 pound cattle. The data also illustrate the effects of drought on feedyard cattle, with a significant spike in BRD mortality during the severe drought of 2012. The increase was especially evident in 600- to 700-pound calves, which went from about 2 percent mortality in 2011 to about 4 percent in 2012. Factors involved probably included drought-related reduction in immunity, inadequate cow-calf nutrition and other environmental conditions such as heat stress and dust in feedyards.

The effects of that single year had implications on the analysis of the trend data. When 2012 was removed from the regression analysis, the rate of increase for mortality across year for all three weight classes of cattle was between 0.04 and 0.05 percent per year. Engler also notes that while the company has increasingly procured cattle directly from ranches, which should reduce BRD risk, they also have engaged in more sorting of cattle in the feedyard to create more uniform marketing groups, which could result in more exposure.

Engler provided data showing the dramatic economic impact of BRD mortality in feedyards, particularly with today’s high market values for cattle. Analysis of Cactus closeout data from 2012 through May 2014 indicates that a 1 percent increase in mortality has a $20.07 per head negative effect on all cattle marketed.

New technologies

Several presenters at the BRDS symposium outlined new concepts and technologies for diagnosing and treating the disease. One of the most challenging aspects of controlling BRD is the difficulty in accurate diagnosis, particularly in its early stages when treatment is most effective. Multiple pathogens and environmental interactions result in a wide range of clinical signs. And some of the classic signs of BRD such as depression, fever or reduced appetite can result from conditions unrelated to BRD. When researchers examine cattle lungs at packing plants, they typically find a low correlation between BRD pulls and actual lung lesions.  

The new “Whisper” electronic stethoscope system aims to change that. During the symposium, Nebraska veterinarian Tom Noffsinger described the system, validation research and its potential application in feedyards and dairies.

Noffsinger notes that in many feedyards, a rectal thermometer is the only objective diagnostic tool used to evaluate cattle for BRD. Most diagnoses rely on subjective observations, and even rectal temperature is not entirely reliable for diagnosing BRD. A conventional stethoscope can significantly improve chute-side diagnostics. Research from Noffsinger’s practice group, Professional Animal Consultation, showed a 34 percent reduction in mortality rates in pulled cattle that were auscultated, compared with non- auscultated respiratory pulls. The data set included more than 500,000 cattle. But even in trained hands, identifying and interpreting specific lung sounds in cattle can be challenging.

The Whisper electronic stethoscope system includes software that interprets lung sounds and measures five different levels of lung health. Researchers spent several years developing the system and validating the scoring system with input from expert veterinarian auscultators. The Whisper lung scores indicate severity, duration and progression of disease, Noffsinger says.

Caregivers can use the information to make objective treatment decisions and evaluate outcomes, potentially leading to reductions in BRD-related losses and more judicious use of antimicrobials.

In a study of over 3,000 cattle, researchers found a 6 percent correlation between body temperature and case-fatality rate, with a confidence interval of 2.5 to 9.5 percent. In contrast, the correlation between the Whisper lung score and case-fatality rate was 79.8 percent with a confidence interval of 78.5 to 81.1 percent.

In these trials, the number of false negatives with fever as a diagnostic test predictor (i.e. those that died and did not have a fever) was 608 head. The number of false negatives with Whisper lung score of “1”as a diagnostic test predictor was 210 head, a reduction of 65 percent. The number of false negatives with a combined fever and Whisper lung score was 102 head – 506 head or 83 percent less than fever alone as diagnostic test predictor and 108 less head than Whisper lung score alone as a predictor of fatality.

Noffsinger says Whisper is neither perfect nor infallible, but its use has resulted in better case definition, improved risk assessment, stratification of cattle by lung score, and targeted antibiotic treatments. The new audio technology, he says, will change the way you “see” BRD. The Whisper Electronic Stethoscope was developed by Geissler Corporation and will be marketed by Micro Beef Technologies.

Selection for disease resistance

Among the complexities inherent in BRD, a genetic component leaves some animals more susceptible, or more resistant, than average. Identifying those animals for selection purposes however, only now is becoming feasible through the use of genomic technology. During conference in Denver, University of California-Davis animal scientist Alison Van Eenennaam, PhD, outlined progress in the nationwide BRD CAP project, a 5-year USDA-funded Coordinated Agricultural Project to address the problem of BRD in dairy and beef cattle. The primary objective of the project is to use the tools of modern genomics to identify cattle that are less susceptible to BRD.

Van Eenennaam says genomic evaluations and genomic-enhanced selection are most useful for genetic traits that are difficult to measure, can only be measured late in life or have low heritability. Disease resistance fits that definition, but the ability to select against disease susceptibility could provide significant economic benefits. She notes, for example, that the dairy industry currently applies genetic selection for mastitis resistance in spite of low heritability and some adverse relationships with other economically important traits.

The BRD CAP project has included two large genome-wide association studies (GWAS), which were conducted using a case/control design on pre-weaned Holstein dairy heifers in one study and Bos taurus beef feedlot cattle in another. Researchers used a calf-health scoring system to identify BRD cases and controls, and used genomic technology such as the Illumina BovineHD 770K Bead Chip for DNA analysis. Through these studies, the researchers estimate heritability for BRD susceptibility ranging from 19 to 21 percent for dairy calves up to 29.2 percent for beef cattle when using numerical scores as a semi-quantitative definition of BRD.

Heritability at those levels could allow significant genetic progress through genomic-enhanced selection. Ultimately, researchers hope to develop genomic breeding values for disease susceptibility to incorporate into selection indices. Van Eenennaam says this process likely will be easier in dairy cattle because of the predominance of the Holstein breed, as accuracy of genomic predictions declines when applied across breeds. Over time, more detailed whole-genome evaluations could provide more accurate across-breed predictions.

Asked whether selection for resistance to BRD could have adverse effects such as increasing susceptibility to other diseases, Van Eenennaam said there probably will be some optimum level of resistance, which could be achieved by removing cattle with the most genetic BRD susceptibility from herds, while continuing to include traits for overall health and performance among selection priorities.

Back to basics

While these new approaches hold great promise, it also became clear the industry could significantly reduce losses associated with BRD by going back to the basics. Hilton says numerous studies have shown preconditioning programs, including nutrition, comprehensive vaccination and weaning on the farm of origin for at least 30 days, can dramatically reduce BRD morbidity and mortality in calves shipped to the next production stage.

Craig Uden, owner of Darr Feedlot near Cozad, Neb., agrees, saying BRD prevention needs to begin at the cow-calf level, and that nothing replaces good pre- and post-calving cow nutrition, good handling practices and a first round of calf vaccines prior to branding or turnout. At Darr, Uden says, buyers pay ranchers a $15-per-hundredweight premium for preconditioned calves.

Hilton says if all stocker and feedyard buyers drew a line in the sand, saying they would no longer purchase high-risk calves at any price, market pressures would dramatically reduce BRD problems. That is not likely to happen though, because some buyers see high-risk calves as a bargain and some ranchers view preconditioning as a cost, rather than an investment.

Hilton stresses the focus should be on educating cow-calf producers on the benefits of early prevention and preconditioning. He suggests that instead of just discussing the buyer-dependent “preconditioning bonus,” veterinarians and the industry should highlight the profit from additional pounds sold and returns per hour invested for the rancher, which are seller-dependent.

Sidebar

Tools for BRD reduction

Purdue University veterinarian Mark Hilton provides the following lists of potential steps for reducing BRD, grouped by their likely impact on diseases incidence.  

Questionable Impact

  • Develop new BRD vaccines or bacterins to give at feedlot entry.
  • Develop new and longer-acting antibiotics.

Potential Impact

  • Increased study on micronutrients that are important for immune function.
  • Improve preweaning nutrition of calves.
  • Discover new viral or bacterial pathogens that cause BRD.
  • Develop new BRD vaccines or bacterins to be given well before entering marketing channels.
  • Discover genetic components of BRD susceptibility.

Likely Impact

  • Improve immunity of calves before arrival at feedlots.
  • Increase age of cattle at feedlot entry.
  • Feed more calves to slaughter at farm of origin eliminating co-mingling.
  • Decrease number of high-risk calves entering marketing channels.
  • Perform all surgeries at farm of origin.
  • Demand by retailers for beef from preconditioned calves based on enhanced animal welfare.

See this article, along with features on PCR testing for parasite diagnosis, lameness in beef and dairy cattle, FMD action steps and on-farm euthanasia in the September digital edition of Bovine Veterinarian.