Once an animal develops symptoms of bovine respiratory disease (BRD), there is more-or-less only one tool in the toolbox – antibiotics. However, as most producers have learned at some point or another, the same product, or the same strategy, doesn’t always have the same effect.
Time to treatment is one of several effectiveness factors, but it’s not the whole story. An antibiotic’s mode of action, as well as ability to move into and eventually be eliminated from the infected area, all contribute to treatment effectiveness. Any additional non-bacterial factors, such as parasites, a viral infection or severely compromised immune system, can also contribute to a BRD outbreak.
Antibiotics enhance, but cannot replace, the immune system’s ability to find and break down bacteria. A weak immune system needs assistance when it comes to fending off multi-layered illness. If an animal shows signs of advanced illness, severely reduced appetite, lowered ears and general lethargy, its system may already be too compromised to work in concert with the antibiotic.
A compromised immune system can be a result of a multi-pathogen assault, but it can also be caused by environmental stressors. Calves coming off the truck may be stressed from thirst, separation from the cow, a sudden change in diet and/or any number of other factors. All of these can lead to loss of appetite, which may be a warning sign of early developing BRD.
Heat, dust, ration changes or drought conditions also erode response to infection. Any nutritional imbalance, a deficiency or surplus of nutrients, can have a similar effect. If an animal develops symptoms then fails to respond to treatment, it may be that the antibiotic used isn’t a good match for the particular pathogen, or it may be the animal is too sick to mount a response at all.
Veterinarians are trained to perform a complete analysis of disease. They can help read the symptoms and find the right antibiotic or determine the environmental and nutritional triggers before the animal is too weak to respond. If the intervention comes too late and the animal dies, then a necropsy can help determine what complications are contributing to the severity of a BRD outbreak. Getting this additional information, and reacting proactively, may be one of the essential keys to protecting the herd as a whole.