Bovine viral diarrhea (BVD) virus can cause severe reproductive losses in cow herds, particularly when a persistently infected (PI) calf survives and continuously exposes the rest of the herd to the virus. During the recent Academy of Veterinary Consultants conference, Michigan State University veterinarian Dan Grooms, DVM, PhD, DACVM, outlined research showing the BVD virus also can cause significant losses during the finishing phase.
Grooms says BVD is a known contributor to bovine respiratory disease (BRD), helping set animals up for infection with bacterial respiratory pathogens. Research also has shown that feeder cattle with positive titers for BVD antibodies, indicating previous exposure on the ranch, have some protection against BRD infection in the feedyard.
Some previous studies looking at feedyard exposure to PI calves have shown an increased risk for BRD, while other studies have not found significant differences.
Grooms and his team conducted three trials to explore relationships between exposure to PI calves, vaccination and BRD incidence in the feedyard. In the first trial, the researchers shipped calves from Alabama to Michigan for feeding. Prior to shipment, the calves were tested and confirmed negative for BVD exposure. One of the trucks included two PI calves, providing exposure during the trip. The other truck had no PI calves. Upon arrival, half of each group were vaccinated for BVD and the other half were not. This created four treatment groups.
- PI-exposed and vaccinated
- PI-exposed and not vaccinated
- PI-free and vaccinated
- PI-free and not vaccinated
Through the finishing period, 25 percent of the non-exposed, non-vaccinated group were treated for respiratory disease, compared with 65 percent of the exposed, non-vaccinated group and 40 percent for the exposed, vaccinated group.
Average daily gains were lowest in the exposed, non-vaccinated group, and feed efficiency also was numerically lower.
Results of the study indicate exposure to BVD-PI calves during marketing, transport or upon arrival correlates with higher incidence of respiratory disease, and that vaccination upon arrival reduces morbidity rates in PI-exposed calves.
Another trial looked at how PI exposure and vaccination on the farm affect feedyard performance. The researchers vaccinated half of a group of 140 calves on the farm two weeks prior to weaning. Some of had previously been exposed to PI calves. After weaning, the calves were shipped to the feedyard where all received a vaccination and were placed in a pen with four PI calves.
The researchers found that the calves with no ranch exposure to BVD and no on-farm vaccination had the most virus isolation after six, eight and 14 days of exposure in the feedyard. They also had the highest morbidity rates. Those exposed on the farm and vaccinated on the farm had the lowest virus isolation and reduced morbidity.
The researchers concluded that exposure to BVD at the cow-calf level, either naturally or through vaccination, provides some protection in the feedyard.
A third study used the same design, except none of the calves were exposed to PI animals on the farm, and thus were negative for BRD antibodies at the beginning of the trial. In this study, 42 percent of the calves not vaccinated on the farm were treated for BRD in the feedyard, compared with 35 percent for the group vaccinated on the farm. The difference in treatment rates in this study was not statistically significant.
Grooms says these studies help illustrate that controlling BVD begins at the cow-calf level with vaccination, biosecurity, identification of PI calves and getting PI calves out of the herd and out of the cattle population.