Cattle producers often assume that vaccinated animals all develop immune response. In reality, however, some individuals build strong immunity, others don’t respond at all, and others fall somewhere in between.
Animals that are sick, malnourished or stressed may build less-than-optimum immunity, for instance. And, of course, young calves with maternal antibodies (passive transfer of immunity from colostrum) may not respond to certain vaccines.
Genetics is another factor that plays a role in vaccination response. Research at South Dakota State University led by Michael Gonda, an assistant professor specializing in animal genetics, is researching the genetics of cattle immunity.
“We’re finding that some cattle respond better than others. Vaccine response is a polygenic trait, which means it’s controlled by a number of different genes. We now have evidence it’s a heritable trait, and are trying to find out how or what genes are involved in determining the animal’s individual vaccine response – whether it’s a high response, average, or low to non-response,” Gonda says.
“There’s a segment of every vaccinated population that doesn’t respond at all to vaccine. These animals lack the capability to respond, mainly because they don’t have the genes to do so. We want to find those genes,” he explains.
The researchers are collecting samples from calves in SDSU research herds, and documenting their responses to vaccination. All calves are vaccinated with a five-way combination vaccine for BVD 1 and 2, IBR, PI³ and BRSV.
“We look at the calves’ response to the BVD portion of the vaccine. Vaccine response is measured by the antibodies produced, utilizing an enzyme-linked immune-sorbent assay (ELISA) test, checking calves 20-30 days after vaccination,” he explains. This gives a good indication of how well the individual calf responded to the vaccine.
“There are some complications. Often, when these calves are being vaccinated, they still have maternal antibodies from colostrum. This can be an issue in the younger calves, so we get a blood sample at the time of vaccination to determine what their maternal antibody concentration was at that time, to use as our baseline,” he explains. The calves being tested are 4-6 months old.
During the past two years, samples have been collected from more than 800 calves and Gonda hopes to eventually have 1,000 samples for the genetic studies.
“We’re still in the process of collecting samples, banking them and running antibody assays. Preliminary analyses found that for each of the calves, the sire is associated with that calf’s response to BVD vaccine,” Gonda says.
The herds being tested have a variety of genetics. Some are purebred Angus, others are predominantly Angus with other breeds and mixes represented. One herd is crossbred. Gonda says it will be interesting to see if there’s stronger immune response in crossbred calves due to heterosis.
“We haven’t yet looked at heterosis in our beef calf samples, but we have results from earlier work with dairy herds. We’ve already compared vaccine response between purebred Holsteins, purebred Jerseys, and crossbreds of those two breeds. This work was in collaboration with Christian Maltecca and other faculty at North Carolina State University (NCSU). In our preliminary work at NCSU, it appears heterosis may play a role, but we are still looking into this,” Gonda says.
The results of this research may be helpful to cattle producers in the future as they seek to select animals that will more likely stay healthy. “Two major implications could come from this research. The first is that it could lead to development of a DNA test for animals that respond more strongly to vaccines, which would enable us to select healthier animals,” says Gonda.
“Secondly, if we can understand how genetics plays a role in vaccine response, it may help immunologists and veterinarians design and develop better vaccines that are more effective for the entire population of animals,” he says.
This research may also benefit other species and add to our understanding of vaccine response in humans as well. A genetic component for response to BVD vaccine would probably also determine vaccination response to other vaccines or disease challenges.