Bovine respiratory disease (BRD) is a worldwide health concern and is the number one disease of stocker, backgrounder, and feedlot cattle in North America. In feedlots in the USA, BRD accounts for 70–80% of all feedlot morbidity and 40–50% of all mortality. In 2011, the US Department of Agriculture's National Animal Health Monitoring System conducted a feedlot study that showed 16.2% of all feedlot cattle were treated for BRD. It is universally accepted that this number is distressingly high and that our industry has the tools available to reduce the incidence of BRD.

The USDA:APHIS National Animal Health Monitoring System collects data on health and health management in livestock and poultry populations throughout the USA in order to provide stakeholders with population estimates to use as benchmarks for comparison, to guide policy development, and to identify research needs and prioritize education efforts. Recent studies of both the beef cattle feedlot industry and dairy heifer rearing operations provided information about BRD occurrence as well as information about prevention and treatment practices used on these operations. While a great deal of effort is dedicated to BRD prevention, there are still opportunities to improve the strategies used. Despite efforts to prevent the disease, BRD continues to be widespread on both of these types of operations.

Mortality during the finishing phase in beef steers has increased over the last 13 years at a rate of 0.05% per year for cattle fed in Cactus Feeders’ operations. A change in the demographics of placements has also occurred, in that heavier weight cattle are being placed as compared to previous years. Morbidity rates are lower, but higher case fatality rates are observed when compared to years when lighter weight cattle were placed. More lung lesions of varying degree are documented at necropsy of new arrivals and there is greater perception of reduced response to therapy in animals identified with respiratory disease. As placement weights have increased, mortality in the early stages of the feeding period has decreased, resulting in a greater proportion of total death loss later in the period. This shift, in conjunction with an increasing long-term trend of total death loss, can lead to the interpretation of higher ‘late day mortality’. Rather than relying solely on observation and distributions of the data, Cactus Feeders believes that the development of a predictive model is better suited to address the potential of ‘late day mortality’ in confined cattle feeding operations.

The primary source of data on bovine respiratory disease (BRD) prevalence in US adult dairy cattle is producer surveys, which estimate that 2.4–2.9% of cattle are affected. This estimate appears low when compared to calculations based on limited data regarding on-farm deaths due to BRD and the number of carcasses at slaughter with severe BRD. These calculations indicate that approximately 3% of dairy cows die on farm or go to slaughter with severe BRD. Not included in these data are cows that are treated for BRD and retained. The primary manifestation of BRD on dairy farms is in calves. Nationwide surveys have estimated that 12.4–16.4% of preweaned dairy heifer calves are affected with BRD, and 5.9–11% of calves are affected after weaning. More detailed prevalence studies have generally included a limited number of small farms, with limited calf age range studied. All studies relied on producer diagnosis. Prevalence in these studies ranged from 0 to 52%, with many cases occurring before weaning, and with BRD being associated with increased calf death rates. BRD affects heifer growth. It appears to have a small effect on age at first calving, and some studies have shown small effects on performance and herd life after calving. First lactation performance of heifers depends on many factors that can obscure the effects of calfhood BRD.

The clinical syndrome of bovine respiratory disease (BRD) continues to be a major challenge in bovine production systems. We are challenged by our ability to predict morbidity in groups of cattle, our ability to accurately diagnose and provide a prognosis for individual cases, and our ability to evaluate the results of preventive and therapeutic interventions in the field when production system data are the sole basis for analysis. However, we are fortunate to have perhaps the highest quantity and quality of negative-controlled, prospective, randomized, and masked clinical trial data for any disease in veterinary medicine. It is nevertheless important to recognize that case definitions in these studies may not be consistent or necessarily externally relevant, and that production data in these studies are often missing.

Bovine respiratory disease (BRD) is the most expensive disease affecting United States cattle. Recently weaned calves are the focus of prevention and treatment research. Identifying affected cattle early in the course of BRD is difficult. Intervention during the early stages of BRD improves treatment outcomes; however, cattle as prey animals are excellent at hiding signs of disease, especially if the caregiver has not gained their trust. Depression, appetite loss, and changes in respiratory character are the principal signs used to identify BRD. Rectal temperatures from cattle pulled for treatment are a final measure of evaluation. Cattle suffering from subclinical BRD frequently escape identification and treatment. Observations of lungs at packing plants for anterior ventral (AV) lesions frequently document higher BRD incidence rates than observed pre-harvest, suggesting subclinical BRD is common. Data from numerous studies document lower average daily gains (ADG) from cattle with AV lung lesions at packing plants that were not treated for BRD compared with cattle with normal lungs. Scoring lung lesions at the packing plant can be a useful tool for gaining insight into BRD incidence. Data indicate that BRD lowers ADG by 0.2 lbs on average, and lowers the USDA Quality Grade by 50 marbling points.

One area where the feedlot industry has been historically weak is the area of BRD “case definition” or diagnosis. Numerous studies demonstrate a weak correlation between lung lesions at harvest and treatment history. This poor track record is due in part to lack of specific chute side diagnostic tools. To analyze the effectiveness of current diagnostic tools (temperature, manual lung scores, and Whisper® lung scores), two data sets were collected. The first evaluated the correlation between rectal temperature, manual lung scores, and case fatality rate in feedlot cattle pulled for BRD. The second evaluated the relative accuracy of Whisper® scores and rectal temperature. Fever was defined as a rectal temperature of 104.5° F or greater. Manual lung scores better correlated with case fatality rate than fever. When fever and Whisper® scores were compared, a Whisper® score of 1 or less better predicted survival than a temperature of less than 104.5° F. The combination of no fever and Whisper® score of 1 or less best predicted survival. The determination of Whisper® score along with rectal temperature in cattle identified with signs of acute BRD can improve case definition, improve risk assessment, and allow more targeted use of antibiotics.

Respiratory disease of young dairy calves is a significant cause of morbidity, mortality, economic loss, and animal welfare concern but there is no gold standard diagnostic test for antemortem diagnosis. Clinical signs typically used to make a diagnosis of respiratory disease of calves are fever, cough, ocular or nasal discharge, abnormal breathing, and auscultation of abnormal lung sounds. Unfortunately, routine screening of calves for respiratory disease on the farm is rarely performed and until more comprehensive, practical and affordable respiratory disease-screening tools such as accelerometers, pedometers, appetite monitors, feed consumption detection systems, remote temperature recording devices, radiant heat detectors, electronic stethoscopes, and thoracic ultrasound are validated, timely diagnosis of respiratory disease can be facilitated using a standardized scoring system. We have developed a scoring system that attributes severity scores to each of four clinical parameters; rectal temperature, cough, nasal discharge, ocular discharge or ear position. A total respiratory score of five points or higher (provided that at least two abnormal parameters are observed) can be used to distinguish affected from unaffected calves. This can be applied as a screening tool twice-weekly to identify pre-weaned calves with respiratory disease thereby facilitating early detection. Coupled with effective treatment protocols, this scoring system will reduce post-weaning pneumonia, chronic pneumonia, and otitis media.

Clinical scoring systems have been proposed for respiratory disease diagnosis in calves, including the Wisconsin (WI) system (McGuirk in 2008) which uses five clinical signs, each partitioned into four levels of severity. Recently, we developed the California (CA) bovine respiratory disease (BRD) scoring system requiring less calf handling and consisting of six clinical signs, each classified as normal or abnormal. The objective of this study was to estimate the on-farm agreement between the WI and the CA scoring systems. A total of 100 calves were enrolled on a CA dairy and assessed for BRD case status using the two scoring systems simultaneously. The Kappa coefficient of agreement between these two systems was estimated to be 0.85, which indicated excellent agreement beyond chance. The simpler design and reduced calf handling required by the CA BRD scoring system may make it advantageous for on-farm use.

Genetics is responsible for approximately half the observed change in performance internationally in well-structured cattle breeding programs. Almost all, if not all, individual characteristics, including animal health, have a genetic basis. Once genetic variation exists then breeding for improvement is possible. Although the heritability of most health traits is low to moderate, considerable exploitable genetic variation does exist. From the limited studies undertaken, and mostly from limited datasets, the direct heritability of susceptibility to BRD varied from 0.07 to 0.22 and the maternal heritability (where estimated) varied from 0.05 to 0.07. Nonetheless, considerable genetic variation clearly exists; the genetic standard deviation for the direct component (binary trait), although differing across populations, varied from 0.08 to 0.20 while the genetic standard deviation for the maternal component varied from 0.04 to 0.07. Little is known about the genetic correlation between genetic predisposition to BRD and animal performance; the estimation of these correlations should be prioritized. (Long-term) Breeding strategies to reduce the incidence of BRD in cattle should be incorporated into national BRD eradication or control strategies.

The Bovine Respiratory Disease Coordinated Agricultural Project (BRD CAP) is a 5-year project funded by the United States Department of Agriculture (USDA), with an overriding objective to use the tools of modern genomics to identify cattle that are less susceptible to BRD. To do this, two large genome wide association studies (GWAS) were conducted using a case:control design on preweaned Holstein dairy heifers and beef feedlot cattle. A health scoring system was used to identify BRD cases and controls. Heritability estimates for BRD susceptibility ranged from 19 to 21% in dairy calves to 29.2% in beef cattle when using numerical scores as a semi-quantitative definition of BRD. A GWAS analysis conducted on the dairy calf data showed that single nucleotide polymorphism (SNP) effects explained 20% of the variation in BRD incidence and 17–20% of the variation in clinical signs. These results represent a preliminary analysis of ongoing work to identify loci associated with BRD. Future work includes validation of the chromosomal regions and SNPs that have been identified as important for BRD susceptibility, fine mapping of chromosomes to identify causal SNPs, and integration of predictive markers for BRD susceptibility into genetic tests and national cattle genetic evaluations.

Fall-weaned calves entering the feedlot experience a variety of psychological and physical stressors, including maternal separation, transportation, social mixing, restraint, and dietary changes. Mixing calves from multiple sources also exposes them to respiratory pathogens at a time when maternal immunity has waned. Using an experimental bovine respiratory disease (BRD) challenge, we analyzed the effects of specific stressors on clinical disease and immune responses following bovine herpes virus (BHV-1/IBR) infection of naïve calves. Transportation stress was compared to either abrupt weaning plus transportation or transportation following a two-step weaning process. Transportation alone significantly (P < 0.05) increased BHV-1 shedding in nasal secretions despite elevated interferon-gamma production in the upper respiratory tract. In contrast, abrupt weaning and transportation, significantly (P < 0.05) increased serum haptoglobin on day 3 post-infection (PI) and blood leukocyte tumor necrosis factor α secretion on day 5 PI. These systemic responses were reduced by instituting a two-step weaning process 4 days prior to transportation and BHV-1 infection. In conclusion, these observations are consistent with earlier studies implicating weaning and transportation as stressors contributing to BRD severity and mortality. Current studies also revealed that different stressors or combination of stressors have distinct effects on host responses to viral infection in naïve calves.

The pathogenesis of bovine respiratory disease (BRD) is determined by a complex interaction of environmental, infectious, and host factors. Environment trends could impact feedlot cattle by increasing their level of stress. The polymicrobial nature of BRD produces synergies between infectious agents that can alter pathogenesis. However, the nature of the host response to these environmental and infectious challenges largely determines the characteristics of the progression and outcome of BRD.

Bovine respiratory disease complex (BRDC) is a major animal health and economic issue that affects cattle industries worldwide. Within the USA, the beef cattle industry loses up to an estimated 1 billion dollars a year due to BRDC. There are many contributors to BRDC, including environmental stressors and viral and/or bacterial infections. One species of bacteria in particular, Mannheimia haemolytica, is recognized as the major cause of severe fibrinonecrotic pneumonia in cattle. M. haemolytica is an opportunistic pathogen that normally populates the upper respiratory tract of cattle, and invades the lower respiratory tract in stressed and/or virally infected cattle by mechanisms that are not completely understood. However, not all M. haemolytica appear to be equally pathogenic to cattle. Thus, a test could be developed to distinguish M. haemolytica genetic subtypes by their propensity to cause respiratory disease, allowing isolation and/or treatment of cattle harboring strains with an increased propensity to cause disease. To that end, the genomes of over 300 M. haemolytica strains are being sequenced.

The neurophysiological response of an animal to stress involves the production of a number of stress-related neurochemicals including the catecholamines norepinephrine and epinephrine. It is generally believed that such neurochemicals belong exclusively to the animal kingdom and that any role such neurochemicals play in the infective process is largely confined to host physiology and immunology-related parameters. This, however, is wholly incorrect as many of the bacterial species that are known to cause infections possess the capacity to not only recognize neuroendocrine hormones produced by the host in response to stress, but also synthesize the very same neurochemicals. Given this, infectious microorganisms are capable of directly responding to the neurochemical outflow resulting from a stress event and initiating pathogenic processes. Although the neuroendocrine environment of the lung following a stress event is not fully understood, it most likely possesses abundant levels of stress-related neurochemicals due to its rich blood supply and rich noradrenergic tissue innervation. The ability of microorganisms to recognize and produce neurochemicals that can influence the host, known as microbial endocrinology, provides for a mechanistic basis with which to examine the ability of stress to influence health and susceptibility to disease.

Resistance is a qualitative interpretation of antimicrobial activity in vitro. Critical to management of bovine respiratory disease (BRD) is the clinical response in vivo. Attempts to connect activity in vitro to response in vivo have been complicated by the complexity of BRD, interpretation of antimicrobial activity in vitro, and inconsistent measures of clinical success or failure. During recent history, the discovery, development, and commercialization of antimicrobials have decreased. In response to resistance, voluntary and imposed restrictions on use of antimicrobials have been implemented. Resistance can be reversed using technology and knowledge of mechanisms of resistance. Perhaps approaches that reverse resistance will be used in clinical management of BRD in the future. The short answer to the question posed in the title is, ‘yes.’ Since antimicrobial drugs were discovered, resistance has been a consideration for selection of treatment of any infectious disease and BRD is not unique. In the opinion of the author, the more important question is, ‘How will antimicrobial resistance of BRD pathogens impact BRD management in the future?’

Bovine respiratory disease (BRD) involves interactions between respiratory pathogens and stressors. Marketing beef cattle in North America frequently involves commingling of cattle from different backgrounds along with various stressors. Veterinarians are faced with unique challenges when designing preventive health care protocols. Research at Oklahoma State University has generated information to assist the practitioner to make more informed recommendations regarding the value of a single vaccination or revaccination in high-risk cattle, and the benefits of management programs at the farm or ranch of origins, particularly in regard to the impact of commingling of cattle from different origins.

Field disease investigations can help to identify patterns of disease that lead to causal hypotheses and, hopefully, effective disease risk management strategies. The most common way of doing this would be to characterize the outbreak by subject, time, and space. One of the perplexing animal health problems on some beef cattle ranches is the occurrence of pneumonia in calves prior to weaning in conditions of little stress and relative isolation. Field investigation of outbreaks of pneumonia in ranch calves prior to weaning has revealed patterns of sporadic illness in calves less than 30 days of age, and rapidly occurring outbreaks in calves 90–150 days of age. We speculate that the causes of these two patterns may be failure of passive transfer resulting in more sporadic cases in very young calves, or a large proportion of the population losing maternal antibody protection (i.e. losing herd immunity) resulting in rapid and widespread onset of pneumonia in older calves.

Bovine respiratory disease (BRD) is a leading cause of morbidity and mortality in dairy calves. As the number of calves being raised on the dairy farm or at a calf-raising operation has become larger, both opportunity and risk have increased. Opportunities for applying economies of size and scale exist in these large dairy calf populations while meeting specific needs of the dairy calf. BRD control requires effective biosecurity and biocontainment efforts, adequate passive transfer of immunoglobulins, a strategic immunization program, and appropriate diagnostic strategies for ongoing disease surveillance. These components are necessary to achieve an evidence-based approach for preventing and reducing severity of BRD cases. Proper nutrition, housing, and environmental management are important for achieving optimal dairy calf health and performance. Good record keeping and analysis of outcomes are needed to document dairy calf health and performance and to efficiently identify new problems that require attention in these large dairy calf populations. Proper management of calves to prevent and control BRD requires careful planning and follow through to achieve those results but will likely pay big dividends in improved calf health and future productivity.