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Taking aim at moving target of BVD

Doug Scholz Published on 23 December 2011

Any novice bird hunter or skeet shooter quickly learns one simple truth – it’s hard to hit a moving target.

But those drawing a bead on clay pigeons or pheasants do have one distinct advantage. They usually have a clear, unobstructed view of their target.

What’s more difficult is to hit a moving target that sneaks around outside of plain sight. And that’s precisely why bovine viral diarrhea virus (BVD) continues to affect a large percentage of beef herds – it lurks around, commonly avoiding detection and changing form every so often in an act of self-preservation.

BVD is a complex disease that’s very difficult to control. Part of the challenge can be attributed to just how prevalent the disease is in U.S. cattle herds.

Sixty to 85 percent of domestic cattle are exposed to the BVD virus and one-half to 2 percent are persistently infected (PI).

As one of the few cattle viruses that regularly mutates, BVD continues to be a moving target for veterinarians and producers.

It consists of hundreds of different viral strains, making it especially difficult to recognize the disease. A further complication is that up to 90 percent of BVD infections are subclinical, meaning infected cattle show no outward signs of sickness.

BVD is particularly devastating because it can affect cattle in every stage of production. Contrary to its name, diarrhea rarely occurs with BVD infections.

Diseases caused by BVD vary from subclinical to highly fatal and are frequently linked to reproductive, respiratory, gastrointestinal, circulatory and immunologic failures.

Economic impact of BVD

The direct and indirect financial losses associated with BVD are difficult to quantify, because many BVD infections go undiagnosed or are misdiagnosed.

However, the annual economic loss in the U.S. is approximately $3 billion – and rising. Estimates from the National Animal Disease Center in Ames, Iowa, have suggested that BVD costs producers $376 million to $1.5 billion in reproductive costs and $360 million in reduced production in feedlots.

Because BVD is an immunosuppressive virus, much of the economic impact is the result of a weakened immune system, which can lead to secondary respiratory infections.

The BVD virus is often a precursor to Pasteurella multocida, Histophilus somni and Mannheimia (Pasteurella) haemolytica, along with other bacterial species.

BVD types and cattle health

BVD strains generally fall into two broad categories – Type 1 and Type 2. BVD viral strains are further classified according to their biotypes: cytopathic (CP) and non-cytopathic (NCP).

According to records from the Animal Disease Research and Diagnostic Laboratory at South Dakota State University, 90 to 95 percent of the BVD strains isolated are NCP, while only 5 to 10 percent are CP.

In addition, recent data from the University of Auburn show that 98 to 99 percent of the field samples diagnosed are NCP BVD. The NCP biotype is also responsible for 100 percent of BVD PI animals, as well as most BVD-induced abortions.

The problem of PI calves

One of the most problematic aspects of the BVD virus is its ability to cause PI calves. PI animals occur when pregnant cows are infected with the NCP BVD virus.

Whether or not a fetus becomes PI depends on the stage of the fetus at the time of infection. PI calves usually occur when unprotected cows are infected between 40 and 120 days of pregnancy.

While they can appear normal, PI calves may expose healthy herdmates to infection because they continually shed the virus through urine, feces and mucus.

PI calves represent the greatest risk as they move through market channels as feedlot animals or replacement heifers.

The devastating results of a PI animal’s presence in a herd can include abortion, early embryonic death, infertility, malformed fetuses, respiratory disease, immunosuppression and the creation of more PI animals.

Keys to BVD control

Gaining control of BVD requires good biosecurity measures – including testing and removal of PI animals – along with effective vaccination.

For maximum herd protection, veterinarians frequently recommend choosing a vaccine that offers broad-spectrum coverage against field strains of both BVD Type 1 and Type 2 genotypes, including NCP protection.

The following management tips can help reduce the health and performance risks associated with BVD.

  • Know your herd’s status: Diagnostic tests are available to identify PI animals. Test calves at birth and be sure to ear-notch any stillborn calves for testing.
  • Cull PI animals: As an industry, we want to reduce the overall numbers of PI calves. Culling PI animals rather than selling them is critical to the health of the industry.
  • Focus on biosecurity: Be sure to test all incoming animals and keep them separate from the rest of the herd until they are confirmed BVD-free.
  • Vaccination: Cows should be vaccinated for BVD before breeding so they have protection on board during gestation. Be sure to use a vaccine that includes coverage for NCP BVD, which is responsible for all PI calves.
  • Learn and educate: Stay on top of BVD outbreaks in your region so you’re aware of outside threats. Educate your staff about BVD and why vaccination and biosecurity are critical to herd health and operational profitability.

U.S. producers have made significant gains by stepping up their herd health programs. By continuing to focus on the highly prevalent diseases like BVD and working closely with their veterinarians, producers will make further gains in animal health and performance.  end_mark

Five reasons why protection against NCP BVD is essential for herd health

  1. NCP is the primary cause of abortions associated with BVD.
  2. NCP is always the cause for BVD persistently infected (PI) calves.
  3. NCP is the major clinical isolate from nearly all BVD outbreaks – more than 90 percent.
  4. NCP is the most common biotype identified in respiratory disease.
  5. NCP infections are the primary reason BVD continues to flourish in the U.S.

doug scholz

Doug Scholz

Director of Veterinary Services
Novartis Animal Health