While the majority of bovine viral diarrhea virus (BVDV) cases 30 years ago were caused by Type 1a, Type 1b has now emerged as the most prevalent subgenotype of BVDV in the U.S., accounting for roughly 70% of reported cases, according to Boehringer Ingelheim.
One reason for the shift is that viruses often mutate to escape detection by the animal’s immune system, but some experts theorize that Type 1b may have gained dominance by taking advantage of gaps in protection left by vaccines that haven’t adequately stimulated immunity against this disease threat, the company said.
Once the virus gains a foothold in an operation, animals that are persistently infected (PI) with BVDV Type 1b expose susceptible cattle to the virus and are considered to be a primary source for maintaining BVDV infections in cattle herds.
“Whether you’re a cow/calf, stocker or feedlot operation, when your cattle are exposed to BVDV, I would say the odds are three to one they’re going to be exposed to Type 1b,” said Dr. John Davidson, senior associate director of beef professional veterinary services at Boehringer Ingelheim. “If you’re a betting person and you take those odds, you’ll want to make sure your vaccine program lines up against that threat.”
In addition to an effective vaccination program, sound prevention strategies frequently utilize herd surveillance for PI cattle and strict biosecurity measures to prevent BVDV from damaging the herd, Boehringer Ingelheim noted.
Good records are the cornerstone of any herd health program, but they’re especially important for identifying potential BVDV issues. “When you start with excellent records, and you recognize changes in reproductive performance, productivity or unexplained illness rates, you can begin to piece together a possible explanation,” Davidson said.
Identifying a problem that could be related to BVDV should trigger surveillance testing. In large operations, veterinarians may start with pooled ear notches or blood samples, which can help determine if BVDV is part of the issue. Any pools with positive results are followed up with individual tests to identify PI calves. All bulls, replacement heifers and dams of PI calves should be tested as well, and positives should be culled or isolated from the rest of the herd, Davidson suggested.
At the cow/calf level, it’s important to minimize exposure of cows and heifers to calves of unknown PI status. “I’ve seen numerous instances where an operation might have cattle with an unknown history on one side of a common fence line and vulnerable pregnant cows on the other, not aware that fence-line contact between pregnant cows and PI calves was what eventually led to more BVDV PI cattle,” Davidson said.
He noted that it is a numbers game: For operations that buy cattle from unknown sources, the odds are good that PI calves will be present. Infected calves can shed large amounts of virus, exposing other cattle at the local livestock market and on the trailer ride to the stocker or feedlot. On arrival, infected animals can leave virus around the feed bunk, in the water trough and through the chute during processing.
That’s why it’s important to quarantine new additions to the herd. “It’s a good idea to keep them in their own group for 14-21 days, test their BVDV status, monitor them for disease and make sure they’re vaccinated before moving those cattle out into the general population,” Davidson added.
According to Davidson, BVDV PI calves are preventable. “This is truly one of those diseases we can impact through selection of the right vaccine and giving it at the right time,” he explained. Producers should work with their veterinarians to choose the right vaccines for the unique disease threats on their operations.
Davidson recommended vaccinating cows with a modified-live virus BVDV vaccine pre-breeding. “It’s important to identify vaccines that have the PI prevention claims clearly indicated on the label,” he said. “Even further, make sure those package inserts also include language about the efficacy of those vaccines against the most common subtype of BVDV, which is Type 1b.”