What is Bovine Respiratory Disease? Part 2: Causes

What causes Bovine Respiratory Disease?

BRD is defined as a "disease complex" or a complex multi-factorial disease as it involves an interaction between several factors -

  • Host factors, or characteristics that make the animal more susceptible to the disease: age, immune status, prior exposure to the pathogens, injury and genetics.
  • Environmental factors: transport, handling, dust, temperature fluctuations, crowding and ventilation.
  • Infectious agents (disease-causing organisms or pathogens) such as
    • Viruses, including the Infectious Bovine Rhinotracheitis (IBR) which often lead to secondary bacterial infections.
    • Bacteria, in particular the three most common; Mannheimia haemolytica, Pasteurella multocida and Histophilus (Haemophilus) somnus. While you may not know exactly which is causing the disease, many BRD cases are multi-organism infections, with more bacteria invading as the disease advances.
    • Parasites, including lungworm.
Any one risk factor may not cause BRD, but in conjunction they can predispose the animal to BRD.

Also, BRD can re-occur due to:
  • The animal not being completely cleared of bacteria during earlier treatments.
  • An on-going infection with resistant population of bacteria.
Learn more: What is Bovine Respiratory Disease? Part 1: Symptoms


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