Getting to know your BRD Pathogens

Bovine respiratory disease complex (BRDC) treatment starts with prevention, for good reason. Implemented properly, a strong health program will generate antibodies against dangerous bacteria and viruses, stimulate a strong immune response and reduce the threat from parasites. However, if these precautions aren’t successful, BRD pathogens can invade and are destructive, opportunistic and quick to develop into dangerous multi-pathogen complexes.

Viruses are often the instigators, if not necessarily the most destructive component, of a BRDC outbreak. While reducing performance on their own, BRDC viruses also weaken cattle’s natural defenses. By treating early with antibiotics, producers may prevent further immune weakening or lung damage caused by bacteria gaining entry to the lower respiratory tract. If treatment comes too late, or is ineffective, the animal will have to fight any secondary infections as well as the virus, for which there is no direct treatment.

Bacteria are numerous even within healthy cattle. One or more of the BRD-related strains, including Mannheimia haemolytica, Histophilus somni or a mycoplasma, are usually present and any immune weakness may result in BRD symptoms. Bacteria condition their environment by producing toxins which damage tissue and disrupt the process of fending off invading pathogens. Mycoplasmas are particularly adept at showing up as secondary infections. All of these pathogens will begin to spread around the cattle herd until the sick animal is isolated. A BRDC breakout may start with one pathogen, but each animal may suffer from a different illness.

Once illness appears, most treatment courses begin with some form of antibiotic. Whether the infection is viral or bacterial, reducing the risk of secondary infections and increased toxin levels helps reduce the burden on the animal. Remember, we can’t directly treat a virus, only make it easier for cattle to fight it off themselves.

Measuring the risk and pathology of the various BRDC pathogens is an ongoing process. For producers, working with a veterinarian can help focus the diagnostic process and find opportunities to improve the herd’s overall health. More information is helping to broaden our understanding of the pathogen complex. It is even starting to overturn some longstanding assumptions of how cattle get sick. Pathogens adapt, but our cattle are changing, too. A good health program, continued vigilance and staying informed are a producer’s most valuable tools to reduce the damage of BRDC.

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