The North American beef cattle industry has endured many changes throughout the years but is encountering some of the most dramatic challenges in history during the first decade of the 21st century. The US beef cattle inventory increased from 1990 to a high of 103.5 million in 1996 and since has declined to a low of 94.5 million on 1 January 2009. Even though economic signals have encouraged the cow herd to increase over the last 5 years, a significant decrease occurred during 2008. It is difficult to determine the precise cost of bovine respiratory disease (BRD) to the industry but it is reported to be greater than US$500 million per year. Data from our practice indicate that losses from BRD over the last 18 years have been characterized by 5-year cycles of decreases and increases. Perhaps it is time for the industry to look for ways to reduce death loss by methods that focus on the animal's response to the pathogens instead of continuing to focus on the pathogens.

The risk of bovine respiratory disease (BRD) has a significant effect on the value of cattle in the marketplace. Calves sold in larger groups have $6.37/45.45 kg more value than those sold as singles or in small groups. Morbidity is higher in unweaned commingled calves than those marketed in groups more than 45 days following weaning. Calves with an aggressive disposition have significantly less value than docile calves, due largely to depressed performance and less carcass value. The value of cattle in the marketplace can be improved by offering larger, uniform lots of cattle that have been weaned at least 45 days. Cattle that suffer BRD in the feedlot have from $23.23 to $151.18 less value than those remaining healthy.

The costs of bovine respiratory disease (BRD) to the beef producer can be estimated by identifying and summing the direct and indirect costs associated with the disease. The major direct costs are attributable to the cost of the feeder, production costs and carcass disposal. The indirect costs are mainly associated with infrastructure and labour.

Respiratory disease is a significant economic burden for United States dairies. Although there has been quality research, there is a need to translate the academic findings to the dairy barn. In particular, there is a need to implement solutions in the context of the economic ramifications of disease management. Plans to combat respiratory disease need to be simple, implemented incrementally and require low ‘management energy’. If respiratory disease is prevented at an early age, this will ensure the greatest chance that the animals will reach their full genetic potential to produce.

Bovine respiratory disease (BRD) is important for the Ontario dairy industry due to the large economic and welfare costs of this disease. Practical science-based management techniques are needed to control and reduce the risk of this disease. Currently, the emphasis on BRD is focused on early detection of disease and prevention. These areas are important but it is not practical to assume this disease will be eliminated in the near future. It is necessary to determine the best practices for caring for sick animals, monitoring their recovery and making changes to their management to facilitate health and recovery. If management changes can be made for animals that are failing to thrive in a current situation, a more complete recovery may be possible and the welfare and economic costs of BRD may be minimized.

The heritability estimates for resistance and/or susceptibility to bovine respiratory disease (BRD) are small, suggesting response to direct selection will be slow. The number of mammalian genetic markers associated with resistance to specific pathogens or improved immunity is increasing and will provide additional information for developing selection criteria for producing animals with an innate resistance to BRD. Environmental and management factors play significant roles in the prevalence of BRD and must be considered in a holistic approach to reducing BRD. Although no single solution for preventing BRD is likely to be discovered in the immediate future, the long-term outlook appears very promising.

The number of cattle operations which manage their livestock as certified organic or as natural is constantly increasing. Common conditions that practitioners often see have bacterial, viral or parasite etiologies. With restrictions on treatments allowed, either by the United States Department of Agriculture (USDA) Certified Organic program or by other niche programs, it would help practitioners to know what is allowable to use and how to approach cases in these settings. This presentation aims to provide veterinarians with an awareness of animal health care when working with organic/natural producers and alternative therapies that are understandable to medically trained professionals.

An animal's welfare should be governed by five freedoms, namely, freedom from hunger and thirst, freedom from discomfort, freedom from pain, injury or disease, freedom to express normal behavior and freedom from fear and distress. If the essence of veterinary medicine is to act like a physician for animals then the profession must be vocal in opposition to production diseases, which can be prevented by changing the system of production.

Bovine respiratory disease (BRD) research has provided significant understanding of the disease over the past 26 years. Modern research tools that have been used include monoclonal antibodies, genomics, polymerase chain reaction, immunohistochemistry (IHC), DNA vaccines and viral vectors coding for immunogens. Emerging/reemerging viruses and new antigenic strains of viruses and bacteria have been identified. Methods of detection and the role for cattle persistently infected bovine viral diarrhea virus (BVDV) were identified; viral subunits, cellular components and bacterial products have been characterized. Product advances have included vaccines for bovine respiratory syncytial virus, Mannheimia haemolytica and Pasteurella multocida; the addition of BVDV2 to the existing vaccines and new antibiotics. The role of Mycoplasma spp., particularly Mycoplasma bovis in BRD, has been more extensively studied. Bovine immunology research has provided more specific information on immune responses, T cell subsets and cytokines. The molecular and genetic basis for viral–bacterial synergy in BRD has been described. Attempts have been made to document how prevention of BRD by proper vaccination and management prior to exposure to infectious agents can minimize disease and serve as economic incentives for certified health programs.

Bovine respiratory disease (BRD) involves complex interactions amongst viral and bacterial pathogens that can lead to intense pulmonary inflammation (fibrinous pleuropneumonia). Viral infection greatly increases the susceptibility of cattle to secondary infection of the lung with bacterial pathogens like Mannheimia haemolytica and Histophilus somni. The underlying reason for this viral/bacterial synergism, and the manner in which cattle respond to the virulence strategies of the bacterial pathogens, is incompletely understood. Bovine herpesvirus type 1 (BHV-1) infection of bronchial epithelial cells in vitro enhances the binding of M. haemolytica and triggers release of inflammatory mediators that attract and enhance binding of neutrophils. An exotoxin (leukotoxin) released from M. haemolytica further stimulates release of inflammatory mediators and causes leukocyte death. Cattle infected with H. somni frequently display vasculitis. Exposure of bovine endothelial cells to H. somnii or its lipooligosaccharide (LOS) increases endothelium permeability, and makes the surface of the endothelial cells pro-coagulant. These processes are amplified in the presence of platelets. The above findings demonstrate that bovine respiratory pathogens (BHV-1, M. haemolytica and H. somni) interact with leukocytes and other cells (epithelial and endothelial cells) leading to the inflammation that characterizes BRD.

Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis and Arcanobacterium pyogenes are all frequently implicated in bovine respiratory disease (BRD). M. haemolytica is considered the most important of the group. These bacteria are commensals in the nasopharynx and establish infection in the lungs of cattle that are subjected to a variety of stresses. Factors that permit adherence to and proliferation in the lungs and factors that cause tissue destruction and inflammation have been identified as having major roles in pathogenesis. These virulence factors include protein adhesins, capsular polysaccharide, outer membrane proteins, iron-binding proteins, lipopolysacharide or lipooligosaccharide, enzymes and toxins. These bacterial products function to evade the immune system, damage the immune system and induce a severe inflammatory response.

Many viruses, including bovine herpesvirus-1 (BHV-1), bovine respiratory syncytial virus (BRSV), parainfluenzavirus-3 (PI3), bovine coronavirus, bovine viral diarrhea virus and bovine reovirus, have been etiologically associated with respiratory disease in cattle. This review focuses on the pathogenesis of BHV-1 and BRSV, two very different agents that primarily cause disease in the upper and lower respiratory tract, respectively.

Advances over the last 20 years in immunology and molecular biology have provided many new tools for identifying the important antigens and new ways to achieve the appropriate immune responses to these antigens. These provide many more options to achieve the best immune response from deletion mutations, subunit antigens, vectors or DNA immunization. These tools are being adopted to screen, discover and produce the appropriate antigens and to deliver them by the optimal method and with novel adjuvants to achieve the appropriate immune response. These developments will result in vaccines for respiratory disease that are safer and more efficacious, and provide greater flexibility for use and administration.

Pharmacodynamics is limited with respect to its ability to provide precise predictions to guide therapy because of complications related to the bound versus unbound state of the agent, tissue versus plasma concentrations, drug degradation over time, variations among microorganisms, and factors associated with the specific environment at the infection site. Antimicrobial susceptibility testing is likewise imprecise when applied to an individual animal; however, it is valuable on an animal population basis.

Industry has made large investments into bovine respiratory disease (BRD) research historically, and will continue to do so, despite the apparent lack of progress, an uncertain regulatory environment, and increased competition for internal resources. Factors such as the growing demand for protein, and the ongoing consolidation and ‘technification’ of the beef sector globally suggest that the industry will continue to demand interventions that prevent disease, are more efficacious, can be easily administered, and positively affect meat quality. New products must also meet the regulatory requirements of safety and efficacy and anticipate the future needs of the numerous stakeholders in the global food chain. Two obstacles in meeting this challenge are the declining interest in food animal medicine, and BRD specifically, and the reluctance to accept new technology at the consumer level.

Despite numerous advances in bovine infectious disease research, bovine respiratory disease (BRD) remains a significant disease threat and a cause of tremendous loss. Renewed efforts and innovative strategies are required to build on the successes of the past to achieve the successes of tomorrow. Continued and improved support of BRD research will prove to be a worthwhile investment. To achieve better coordination and more efficient use of resources, the following supportive actions should be considered. There should be coordination of integrative teams through an over-arching agency (United States Department of Agriculture (USDA)) to provide peer review and priority review for available public research funds. This would include use of development grants (as seed and matching funding) available to public/private partnerships. Testing and validation of new procedures in production settings (providing more than cost analyses) should be strengthened. Publication of studies should be promoted and old links between clinicians, diagnosticians and basic researchers should be re-established. Sets of ‘best practices’ should be published. Programs to support both basic and applied research through graduate fellowships, residencies, workshops and start-up funding for young research scientists should be strengthened. Sustained funding to train the next generation of research investigators should be addressed as a critical need.