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.

Pasteur described an organism causing fowl cholera in 1880. In 134 years we have progressed from crude vaccines for Pasteurella, to some refined vaccines, to a name change (Mannheimia), to autogenous vaccines (back to crude). In the last 25–30 years, we have attempted to mitigate the problem of bovine respiratory disease with antimicrobials and subsequently have a high incidence of multi-drug resistance. All of these attempts have resulted in little if any improvement in morbidity/mortality. Is it time to focus on the animal's response or lack of response to infectious pressure? Instead of focusing on the 10–50% morbid cattle should we focus on the 50–90% that are not compromised and determine why they stay healthy under the same environmental conditions?

Cow–calf enterprises in the USA are widely divergent in size, locale, resource availability, management skill, and market focus. Furthermore, variation exists in dependence on the cow–calf enterprise as a primary source of income, perception about the utility of a particular management practice or technology, and assessment of cost: benefit resulting from implementation impact decisions. Enterprises with larger cow inventories, greater dependence on income from the cattle enterprise, and that retain ownership further into the supply chain beyond the cow–calf operation are more likely to institute management protocols such as vaccination programs, defined calving seasons, and reproductive technologies. Successful cow–calf managers place the highest priority on herd nutrition, pasture and range management, herd health, financial management marketing, production management, and genetics. Management practices are more likely to be adopted when they align with a manager's perception of the utility, labor availability, favorable cost: benefit outcomes and profit motivation.