Editor’s note: Part 1 in a BVDV series

Bovine viral diarrhea virus (BVDV) is unusual in that it can negatively affect all ages of cattle, as well as every segment of beef production from seedstock, cow-calf, stocker operations and feedlots. It costs the industry in reduced pregnancy rates, increased abortions and stillbirths, increased death loss prior to weaning and losses in stocker and finishing operations after weaning. Because of this, it can have an impact on any type of veterinary practice you may have. And though this discussion will be limited to beef, BVDV can also play a significant role on dairy operations.

As a result of the economic and health impact that BVDV can have on operations, in 2001 the Academy of Veterinary Consultants (AVC) developed a position statement on BVDV (see sidebar), and then followed up in 2003 with BVDV Decision/Management Guidelines for the beef industry. These guidelines, which will be explored in subsequent articles, offer testing and management strategies for high-  and low-risk cow-calf herds, BVDV monitoring strategies and guidelines for stocker and feeding operations.

“Because BVDV affects every segment of the beef cattle industry, effective control strategies must be based on communication between segments, and education that reaches veterinarians involved in mixed-animal, cow-calf, feedlot and even dairy practice,” says Bob Larson, DVM, PhD, University of Missouri.  “The AVC saw that a position statement could help focus industry attention on a disease with both high cost and emerging, effective control strategies.”

 

Dale Grotelueschen, DVM, MS, says the industry has not focused enough on the problem of persistent BVDV infection.

Dale Grotelueschen, DVM, MS, Pfizer Animal Health and chair of the AVC’s ad hoc BVD Control/Eradication Committee, says the position statement and guidelines were discussed at length by the AVC. “The perceived large and far-reaching impacts of BVDV on the beef industry at all levels of production prompted the position statement to stimulate action in all segments to deal with BVDV losses.”

Larson adds that though BVDV has been recognized as an important disease of cattle for many years, control and prevention of the disease has not been particularly successful. “Improved understanding about the role of the persistently infected (PI) animal as a BVDV reservoir and the development of new diagnostic tests such as immunohistochemistry, polymerase chain reaction  and antigen-capture ELISA, have created an opportunity to evaluate new control strategies for this disease that were not feasible in the past.”

 

Bob Larson, DVM, PhD, says the industry needs to focus on this disease that has both an economic impact and effective control strategies.

Education is fragmented
While there is still need for more economic data, available information indicates significant economic loss incurred by the industry. Methods to address control are being improved as the industry conceptualizes what can and needs to be accomplished. “Prevention of PI animals in the beef population is the key component,” says Grotelueschen. “The industry has not yet focused well enough on this issue.”

Typically, education about diseases and control options are somewhat fragmented. Biologic companies may focus educational efforts on their vaccines and their role in disease control. Laboratory diagnosticians will likely focus on the tests that their lab offers, and those tests’ role in the control of disease. Researchers may add information about the disease agent, an animal’s response to infection, or the epidemiology of the disease. “A coordinated educational effort that considers many areas of expertise about BVDV and cattle production could help veterinarians and their producers develop on-farm and on-feedlot plans of action to diagnose, control and prevent BVDV as a cause of economic loss,” says Larson.

In order for control programs to be tailor-made for individual operations, the principles of BVDV control must be understood. For these reasons, the BVDV guidelines were developed. Grotelueschen says it took many individuals from a variety of disciplines, including virologists, practitioners, diagnosticians, epidemiologists, academic researchers and others to develop guidelines and strategies that addressed the economic and practical issues of BVDV testing and control programs.

“Veterinary practices should consider development of written BVDV control plans – rather than just vaccination recommendations – using available scientifically valid information,” he adds. “Beef operations also should implement BVDV control plans based on their goals as well as what can be accomplished in individual herds. These plans should be driven by economics and what can physically be accomplished given the extensive variability from operation to operation as well as management and geographic variations across the U.S.”

AVC BVDV position statement
Position statement on bovine viral diarrhea virus by the Academy of Veterinary Consultants:

The beef and dairy industries suffer enormous loss due to effects of bovine viral diarrhea virus (BVDV) infection. The highly mutable nature of BVDV and the emergence of highly virulent strains of BVDV contribute to limited success of present control programs. Also, persistently infected cattle are the primary source of infection and effective testing procedures are available to identify those infected carriers.

Therefore, it is the resolve of the Academy of Veterinary Consultants that the beef and dairy industries adopt measures to control and target eventual eradication of BVDV from North America.

Approved by majority vote of membership, November 2001

BVDV misconceptions

  • Persistently infected (PI) calves will be killed by modified live virus (MLV) vaccination. Fact: Controlled experiments have not been able to induce morbidity or mortality in PI calves following MLV vaccination. However, case reports indicate that MLV vaccination can cause a PI animal to become moribund or to die – though far less than 100 percent are negatively affected.
  • PI calves are thin, have rough haircoats and are poor-doers. Fact: While many PI animals are unthrifty, reports have indicated up to 50 percent will appear normal and may enter the breeding herd or feedlot pen in excellent condition. PI calves cannot be identified visually.
  • Calves are PI because their dam is PI. Fact: Recent research has shown that 7 percent of PI calves’ dams were PI, the other 93 percent of calves have dams with a normal immune response to BVDV and are not persistently infected.
  • The greatest cost associated with a PI calf is the death of that calf. Fact: The reproductive loss associated with lower pregnancy proportions, more abortions and higher calf mortality are the greatest economic costs of exposure to PI animals. In addition, increased morbidity, treatment costs, treatment failure, and reduced gain in feedlot or stocker penmates greatly exceed the cost of PI death in feeder cattle.
  • BVDV problems will always be obvious. Fact: If BVDV was introduced into the herd via a PI animal several years previously, after an initial period of noticeable losses, the herd may currently experience only low reproductive loss and BVDV-associated morbidity. This low loss, however, may not be compatible with economic sustainability.
  • BVDV won’t affect my herd because I vaccinate. Fact: The tremendous amount of virus secreted by a PI calf can overwhelm a level of immunity that is protective under less severe exposure. There are documented cases of herds with vaccination protocols in place for several years that have endemic BVDV because of the presence of PI animals.

These BVDV misconceptions were developed and provided by the Academy of Veterinary Consultants.

 

A fetus that is infected from its transiently or persistently viremic dam prior to formation of a competent immune system can become persistently infected with the virus.

AVC BVDV Decision/Management Guidelines for Beef Cattle Veterinarians

  • Bovine viral diarrhea virus (BVDV) can cause a variety of clinical and subclinical reproductive, enteric and respiratory syndromes, and immune dysfunction.
  • BVDV is unique in that a fetus that is infected from its transiently or persistently viremic dam prior to formation of a competent immune system can become persistently infected (PI) with the virus.
  • PI cattle will shed BVDV from body secretions throughout their life.
  • PI cattle are considered the primary reservoir for BVDV in both cow herd and feedlot situations.
  • A current estimate is that about 10 percent of beef cow herds have at least one PI animal, and about 0.25 to
  • Veterinarians should have a surveillance strategy to determine level of herd risk for the presence of PI animals (high verses low risk).
  • Herds that are considered high risk for containing PI animals should utilize laboratory tests to do whole-herd screening to find all PI animals and then remove them.
  • PI cattle should be removed from herds immediately and marketed directly to slaughter or euthanized. BVDV is not a human health risk, but PI cattle are a health risk to other cattle and are often in poor health themselves.
  • Vaccination alone will not solve BVDV.

This information was developed and is provided by the Academy of Veterinary Consultants.