Bovine respiratory disease (BRD), also known as shipping fever pneumonia or undifferentiated fever, is a respiratory disease of cattle. BRD has a multifactorial etiology and develops as a result of complex interactions between environmental factors, host factors, and pathogens. BRD is the most common and costly disease affecting the North American beef cattle industry.
Pearls & Pitfalls
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Environmental factors (eg, weaning, transport, commingling, crowding, inclement weather, dust, and inadequate ventilation) serve as stressors that adversely affect specific and nonspecific host defense mechanisms of the host animal. In addition, certain environmental factors (eg, crowding and inadequate ventilation) can enhance the transmission of infectious agents among animals.
BRD is most commonly associated with the transport and assembly of large groups of recently weaned calves into feedlots, hence its alternate name, shipping fever pneumonia. Morbidity in these feeder calves often peaks within 45 days after feedlot arrival. Morbidity rates can approach 35–50%, and case fatality is 5–10%; however, morbidity and mortality rates strongly depend on the array of risk factors present in affected animals.
The use of broad-spectrum antimicrobials labeled for BRD is the primary treatment, with macrolides and phenicols most commonly used as first-line treatment. Prevention and control are achieved via vaccination programs, preconditioning, identification and treatment of subclinically affected animals, and biosecurity.
Many infectious agents have been associated with BRD. This disease can be caused by a variety of bacterial pathogens (eg, Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis) and viral pathogens (eg, bovine herpesvirus 1, parainfluenza-3 virus, bovine viral diarrhea virus, and bovine respiratory syncytial virus). An initial pathogen (eg, a virus) can alter the animal’s defense mechanisms, allowing bacterial colonization of the lower respiratory tract.
Etiology of Bovine Respiratory Disease
The pathogenesis of bovine respiratory disease involves stress factors, sometimes coupled with viral infection, that result in suppressed immune defenses and bacterial proliferation in the upper respiratory tract. Subsequently, these bacteria colonize the lower respiratory tract and cause bronchopneumonia with a cranioventral distribution in the lung. Many of the bacteria and viruses involved are commensal organisms of the upper respiratory tract and can be isolated from a proportion of healthy animals.
Multiple stress factors contribute to the suppression of host defense mechanisms in cattle. Weaning is a noteworthy stressor, and the incidence of this disease is highest in recently weaned calves. Transportation over long distances serves as a stressor that can be associated with exhaustion, starvation, dehydration, chilling, and overheating, depending on weather conditions. Additional important stressors include passage through auction markets; commingling, processing, and surgical procedures on arrival at the feedlot; dusty environmental conditions; and nutritional stress associated with a change to high-energy rations in the feedlot. (See discussions of BRD-associated viral infections and bacterial pneumonia.)
Viruses associated with BRD include the following:
bovine herpesvirus 1 (BHV-1)
parainfluenza-3 virus (PI-3)
bovine viral diarrhea virus (BVDV)
bovine adenovirus
bovine coronavirus
Bacteria associated with BRD include the following:
Mannheimia haemolytica
Pasteurella multocida
Histophilus somni
Mycoplasma bovis
Bibersteinia trehalosi
Control and Prevention of Bovine Respiratory Disease
Prevention of bovine respiratory disease should focus on decreasing stressors that contribute to its development. Cattle should be assembled rapidly into groups, and new animals should not be introduced to established groups. Mixing of cattle from different sources should be avoided or minimized if possible; however, in the North American beef industry, this risk factor is almost unavoidable for large intensive feedlots.
Transport time should be minimized, and rest periods, with access to feed and water, should be provided during prolonged transport. Calves should ideally be weaned 2–3 weeks before shipment, and surgical procedures, such as castration and dehorning, should be performed before transport; however, the availability of these “preconditioned” calves is quite limited.
Dietary adaptations are critical. Specifically, cattle should be introduced to high-energy rations gradually, because acidosis, indigestion, and anorexia may inhibit the immune response. Vitamin and mineral deficiencies should be corrected. Dust control measures should be used.
Metaphylaxis with injectable long-acting antimicrobials (eg, oxytetracycline, tilmicosin, florfenicol, gamithromycin, tildipirosin, and tulathromycin) has been widely adopted as a control measure administered on arrival to cattle at high risk of developing shipping fever pneumonia. Metaphylaxis on arrival has been shown to substantially decrease morbidity rates, improve rate of gain, and, in some cases, decrease mortality rates. Mass medication in feed or water is of limited value because sick animals do not eat or drink enough to achieve inhibitory blood levels of the antimicrobial, and many of these oral antimicrobials are poorly absorbed in ruminants.
Once cattle arrive, processing usually involves administration of modified live virus vaccines against viral antigens and bacterial components of shipping fever pneumonia; however, several meta-analyses have highlighted that minimal evidence exists to support vaccination at arrival for reducing the incidence of BRD. This is likely because cases of pneumonia often occur during the first 2 weeks after arrival, and these on-arrival vaccines might not have adequate time to stimulate complete immunity in all individuals. When possible, vaccinations against viral and bacterial components of shipping fever pneumonia should be administered 2–3 weeks before transport or earlier.
The control and prevention of BRD in dairy heifers is discussed under Enzootic Pneumonia of Calves.
Key Points
Bovine respiratory disease (BRD) is the most common and costly disease affecting the North American beef cattle industry.
BRD risk factors include weaning, transportation, adverse weather, commingling, and stressful events such as dehorning and castration.
BRD is caused by suppressed immune responses and initial viral infection, which allow colonization of the lung by commensal upper respiratory tract bacteria.
Preconditioning, minimizing mixing, vaccination for BRD pathogens, and metaphylaxis for high-risk animals are major control methods.
Broad-spectrum antimicrobials labeled for BRD are the primary treatment.
For More Information
Key elements for implementing antimicrobial stewardship plans in bovine veterinary practices working with beef and dairy operations. American Association of Bovine Practitioners.
Joint AABP-AVC judicious therapeutic use of antimicrobials in cattle. American Association of Bovine Practitioners.
O’Connor AM, Hu D, Totton SC, et al. A systematic review and network meta-analysis of bacterial and viral vaccines, administered at or near arrival at the feedlot, for control of bovine respiratory disease in beef cattle. Anim Health Res Rev. 2019;20(2):143-162.
