Editor’s note: Last in a series on bovine lung immunology.
Boosting lung defenses can include things like low-stress handling and timely use of respiratory vaccines. Dozens of vaccines are available for use in cattle but you can’t get “immunity in a bottle” without strategic timing and proper management.
If the viral infections are the first ones to start compromising the innate defenses, then clearly immunity to the viruses can play a very important role in minimizing the risk of fatal respiratory infections, says Philip Griebel, DVM, PhD, Vaccine and Infectious Disease Organization, University of Saskatchewan. “Vaccines are not a magic bullet, but what they’re doing is raising the threshold of disease susceptibility. They will increase the threshold for an effective challenge dose. Animals need to be exposed to a greater amount of virus for a greater period of time to overcome immune defenses, before the virus starts to impact lung defenses.” Vaccines can also decrease virus transmission within a group, so they can individually raise the threshold of disease susceptibility for individual animals as well as enhance herd immunity by decreasing the efficiency of virus transmission.
Breck Hunsaker, DVM, PhD, Livestock Consulting Services and Horton Research Center, Wellington, Colo., says there is broad support and use of viral vaccines by feedyard managers; however, some feedyards might rely too much on them, based on reported research that questions vaccine efficacy. “Some of our feedyard managers want to vaccinate and revaccinate and revaccinate, if you let them, with viral vaccines. You have to remind them that timing of administration is critical.”
But vaccines alone can’t do it, and can be overwhelmed. Feedlot vaccination includes onset of immunity, magnitude of response, and duration of immune protection. Vaccines have to be delivered strategically relative to the risk period. “Inducing an immune response isn’t sufficient,” Griebel states. “We have to think about the idea of protective immunity. If we vaccinate on arrival, is that too late? It will depend on the exposure. There is now evidence that some of the modified-live viral vaccines can induce protective immunity within five days. But the effectiveness of this vaccination will depend on where those calves are in that infection cycle. We need to think about vaccines very strategically, relative to risk period.”