Bovine respiratory disease (BRD or pneumonia) remains one of the primary infectious diseases in cattle. Advances in technology have greatly enhanced the quality of vaccines and antibiotics available for prevention and treatment of BRD.
But despite these efforts, sickness and death rates have changed very little, if at all.
In a disease outbreak, we treat "sick” calves. What percentage of animals are sick but not detected? What percentage are treated that were not necessarily sick?
When these numbers are analyzed, there is a lack of correlation between cattle treated for BRD and lung lesions present in many studies. Cattle with no lesions after treatment may be success stories or have had unnecessary treatments. Cattle that have untreated lesions may be BRD victims prior to the study or were not identified as being sick. We can't evaluate vaccine effectiveness if we cannot identify sick calves.
A successful vaccine program should take into account different levels of disease. Subclinical disease is often more economically important than the cattle identified as "sick.” The act of giving a vaccine does not always equal a successful vaccination program.
Why do vaccines fail?
Failure can be defined as a single animal getting sick or the entire group suffering from subclinical illness. In certain situations, either of these definitions can be correct.
In the case of blackleg vaccine, we expect nearly 100% protection. When dealing with BRD, we accept partial control of the disease and a decrease in severity.
Our goal is to raise immunity, lower disease challenges and not allow the two to cross. In a production animal setting, however, we must look at the economic feasibility of the plan we implement. Is it realistic to isolate animals while we immunize and screen each one for disease before putting them back into the general population? There are many obstacles between us and our goal of keeping calves well.
Even the most effective vaccine is only useful if it is handled and administered properly and given in a timely manner. One problem I see is the purchase of preconditioned cattle that are then commingled with "green” cattle. This is sure to result in the failure of
the preconditioned cattle.
As the nonvaccinated cattle begin to show clinical signs of disease, there is an exponential increase in the amount of pathogens (disease-causing organisms) in the environment.
Calves vaccinated on arrival at a backgrounder or feedlot will generate unique timing issues. These calves often have been incubating the pathogens for several days. A vaccine is then given under extremely stressful conditions and expected to protect the calf from a disease cascade that is already in motion.
It is our challenge to manage a multifactoral process and move the window of protection in favor of the cattle. This can be done by either raising the level of immunity or lowering the level of disease. In most cases, it takes both. There are many management paradigms that need to be addressed to influence the way cattle are handled in the future.
DAN GOEHL, DVM, and his wife own Canton Veterinary Clinic in Canton, Mo., working with stocker and cow–calf beef operations. He is also a partner in management and marketing of beef cattle. E-mail him questions and comments at email@example.com.