Section 3 | Bovine Respiratory Disease in Feedlots

What is Causing Bovine Respiratory Disease?

Why are Cattle Prone to Developing Respiratory Disease?

The anatomy of the lungs in cattle make them more prone to developing respiratory disease. Cattle require a higher level of oxygen compared to other species. In order to meet that requirement, they need to take more respirations per minute. This high air flow allows pathogens, such as bacteria, viruses, and other contaminants, to enter deep into the lung tissue. It is here where they can trigger infection. This is an important aspect of what makes cattle highly susceptible to developing pneumonia.

What are the Pathogens Responsible for Causing Respiratory Disease?

Viruses

Some of the common viruses responsible for BRD include infectious bovine rhinotracheitis (IBR), bovine parainfluenza 3 (PI₃), bovine respiratory syncytial virus (BRSV), bovine viral diarrhea virus (BVDV) and possibly bovine coronavirus. These viruses cause damage to respiratory tract defenses by damaging the fine hairs that sweep debris out and can reduce immune responses. Viral infections can promote secondary bacterial infections, in addition to causing severe disease on their own.

Bacteria

Bacteria that can cause BRD include: Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, and Mycoplasma bovis. Many of these bacteria can be found in healthy cattle in the upper portion of their respiratory tracts. To establish an infection, they need to travel lower in the respiratory tract – the lungs. When defenses are weakened – by viral infections, stress, nutrient changes, or environmental conditions – bacteria can travel lower down into the respiratory tract and cause disease. Once a bacterial infection is established, bacteria can cause massive inflammation and damage to the lungs²⁰.

How Pathogens Cause BRD