Bovine respiratory disease (BRD) is an infectious disease complex and one of the most common causes of morbidity and mortality in stocker and feedlot operations. Understanding the many factors that contribute to the BRD complex is an important step for producers to take in managing the disease. When BRD hits, a perfect storm of stress factors, virus agents and bacteria are at play in the animal’s respiratory system.
“There are multiple layers of the immune system protecting the respiratory tract, and once we compromise any one of them, we have the potential for a problem,” explains Daniel Scruggs, DVM, DACVP, Pfizer Animal Health. “Compromise two or more with a mix of stress, viral infection and bacterial infection and you are starting down a difficult road.”
Stress factors, such as weaning and transporting, commingling and crowding, and inadequate nutrition, usually set the stage for BRD by reducing the animal’s disease resistance. Scruggs notes that castration and dehorning are some of the main stressors on the immune system, so producers should do these as early as possible to minimize blood loss and allow for a faster immune system recovery. Other factors like transition to new climates, heat stress, access to water, and dust also contribute heavily to the complex.
To reduce the stress factors that contribute to BRD, Scruggs recommends weaning and vaccinating prior to shipment, minimizing commingling by buying cattle from one source, giving cattle room to spread out, minimizing dust, maximizing water availability and avoiding gastrointestinal disturbances by slowly incorporating higher concentrate feed into their diets.
“Producers should always keep in mind the number of cattle they can effectively manage and not purchase more cattle than they can look out for,” Scruggs says. “Make sure you match your type, class, and risk level of cattle to the amount of available time and resources on your operation.”
Managing viral agents
As these factors place stress on the immune system and stack on top of each other, the door is open for viral and bacterial agents to invade. A primary viral infection of the upper respiratory tract is often the next step in the BRD complex.
“Anything that improves bacteria’s ability to attach to respiratory mucosa, proliferate and migrate down into the lung impacts the respiratory tract and makes it susceptible to colonization with a wide variety of bacteria,” Scruggs says. “The viral agents are probably the most effective at compromising the respiratory defense mechanisms to allow bacterial BRD to flourish, but there are other factors that may be as effective.”