Griebel explains that work done by Richard Harland indicated that if vaccines are given in two different sites, such as opposite sides of the neck, there isn’t interference. “You can give them at the same time and not have interference. I think it’s important that people know that they can give both vaccinations if they are at separate sites.” Griebel notes that this work was done with a modified-live IBR/PI3 only.
The ability to neutralize leukotoxins and endotoxins are critical for success when using bacterins, adds D. Scott McVey, DVM, PhD, Veterinary Diagnostic Center, University of Nebraska. That’s where we’ve seen improvement over the last 20 years, like the improvement with the Mannheimia bacterin/toxoids. They’re much better than they used to be. Beyond that, antibodies to many different somatic factors that potentially enhance clearance are important. There are a lot of disclaimers and caveats. We’ve already talked about the weaknesses of bacterial challenge models. We take normal animals and, for experimental purposes, put a ton of bacteria down in the respiratory tract, and then look at usually what counts for registration of a vaccine — comparative lung lesion scores in vaccinates and non-vaccinates. Antibody titers and serologic responses don’t often correlate all that well to that protective response.”
But even under the best of circumstances, what you see is a reduction of 50% to 80% in the lung lesion scores, McVey says. “It’s not sterilizing immunity and it is generally not very effective. On the other hand, most immune responses, under optimal circumstances to viral vaccines — BHV1, BVD — are pretty good. You can knock down shedding and viremia to almost zero.”
If you compromise the timing of the administration strategically, if you compromise the immune system, it’s not surprising that cattle get overwhelmed with the bacterial infections, McVey says. “We have much better vaccines than they used to be. There is a real research opportunity to define clinically relevant challenge model systems for Histophilus somnus.”
Immunology and treatment
Treatment of bovine respiratory disease hits a feedlot hard economically in drug cost, labor, and performance and mortality of cattle. Sometimes treatment is a guessing game when it’s unknown which pathogens are to blame, and the wrong treatment can be of further detriment to the animal.