Bovine respiratory disease

Bovine Respiratory Disease (BRD), commonly referred to as "shipping fever," is a complex, multifactorial disease affecting the lungs of cattle. It is the leading cause of morbidity and mortality in beef and dairy cattle industries, significantly impacting animal welfare and economic profitability. BRD is typically associated with a combination of viral and bacterial pathogens, environmental stressors, and host factors.

Etiology

BRD results from the interplay of various viral and bacterial pathogens. Common viral agents include Bovine Herpesvirus 1 (BHV-1), Bovine Respiratory Syncytial Virus (BRSV), Parainfluenza-3 Virus (PI3V), and Bovine Viral Diarrhea Virus (BVDV). These viruses can compromise the respiratory tract's defenses, making it more susceptible to secondary bacterial infections. The primary bacterial pathogens involved in BRD are Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis.

Pathogenesis

The pathogenesis of BRD is a complex process that begins with the stress-induced suppression of the immune system, followed by viral infection which damages the respiratory epithelium. This damage facilitates the colonization and proliferation of bacterial pathogens, leading to a severe inflammatory response in the lungs. The combination of viral and bacterial infections, along with the inflammatory response, leads to the clinical signs associated with BRD.

Clinical Signs

Clinical signs of BRD can vary but often include increased respiratory rate, coughing, nasal and ocular discharge, fever, lethargy, and reduced appetite. In severe cases, BRD can lead to pneumonia, which can be fatal if not promptly and effectively treated.

Diagnosis

Diagnosis of BRD is based on clinical signs, history of exposure to risk factors, and laboratory tests. Laboratory diagnostics can include polymerase chain reaction (PCR) tests for viral pathogens, culture and sensitivity tests for bacterial pathogens, and serological tests to identify previous exposure to specific agents.

Treatment

Treatment of BRD typically involves the use of antibiotics to combat bacterial infections and supportive care to alleviate symptoms and support recovery. The choice of antibiotic should be guided by culture and sensitivity testing to ensure efficacy against the specific pathogens involved. In cases where viral pathogens predominate, supportive care and prevention of secondary bacterial infections are key.

Prevention

Prevention of BRD involves a multifaceted approach including vaccination against key viral and bacterial pathogens, management practices to reduce stress and improve immunity, and biosecurity measures to prevent the introduction and spread of infectious agents. Proper nutrition, weaning strategies, and environmental management are also critical components of a comprehensive BRD prevention program.

Economic Impact

The economic impact of BRD on the cattle industry is significant, with losses attributed to reduced growth rates, increased mortality, and the costs associated with treatment and prevention. It is estimated that BRD costs the U.S. cattle industry more than $1 billion annually.