Washington Animal Disease Diagnostic Lab

Additional Information

What is BVDV?
Bovine Viral Diarrhea Virus (BVDV) is one of several world-wide pestiviruses known to infect domestic and wild ruminants, camelids, and swine. For cattle producers the virus causes economic losses through decreased weight gains, decreased milk production, reproductive losses, and death. There are many BVD virus types (cytopathic and non-cytopathic). BVDV typing does not predict disease severity, and all BVDV types are detected by current test methods. There are two categories of BVDV infection.

• Transient (acute) infection (“TI”)
   Short term (weeks)
   Acquired after birth
   TI cattle become immune and clear virus
   >95% of BVD infections are TI
   TI cattle minor source of virus spread in herd
• Persistent (chronic) infection (“PI”)
   Life long infection
   Acquired in utero. Thus, only fetal infection results in BVD-PI.
   PI cattle never become immune
   <5% of BVD infection are PI
   PI cattle major source of virus spread in herd!
   Over 90% of BVD-PI calves are born from normal dams (no prior BVDV exposure)

What is BVD clinical disease?
Most BVDV infection problems in cattle herds go unnoticed since 70-90% of BVD infections are subclinical (do not result in observable disease). When present, the most common disease caused by BVD virus infection in cattle herds is poor reproductive performance including, abortions, poor conception rates, stillbirths, and weak calves. In addition, BVD virus infection causes suppression of the bovine immune system resulting in increased susceptibility to other infectious diseases. In cow-calf herds the immunosuppressive effect of BVD is normally noticed as increased calf death loss (from scours and pneumonia) and poor weaning weight. In feedlot animals this is noticed primarily as increased death loss and incidence of respiratory disease (pneumonia). Lastly, BVD virus infection alone can cause diarrhea with oral ulcers and bleeding disorders.

How is BVDV transmitted?
The main source of BVDV in cattle herds is BVD-PI animals. Virus in BVD-PI animals is shed in all body secretions including nasal discharge, saliva, tears, milk, feces, urine and semen. Transmission occurs via ingestion, inhalation, and fomites (non-living sources such as boots and vehicles). Some commons ways BVDV can enter cattle herds are:

Purchasing replacements at auction
Purchase of pregnant cow/heifer with PI calf
Introducing replacements or show stock without quarantine
Failure to maintain BVD vaccination program
Failure to test replacements for BVD PI
Contaminated semen or embryos
Borrowed or escaped bulls

Why test and remove BVD-PI animals from a cattle herd?
Persistently infected (PI) cattle are the major source of BVD infection and disease in cattle because they shed huge amount of BVD virus throughout their lives. The major economic loss associated with BVD in cow-calf operations is loss of income due to loss of calves either before birth (abortion), at birth (weak calves) or between birth and weaning (BVD-induced immunosuppression make calves more susceptible to common calf disease such as pneumonia and scours). Thus removal of BVD-PI animals from a cattle herd should result in:

Improve reproductive performance in herd
Improve pre-weaning performance in herd (weaning weights and calves weaned)
Lower calf treatment costs and calf death loss
Provide more marketable cattle (BVD free certified herd status)

Can BVDV infection be eradicated from a herd with vaccination?
No, BVD vaccination alone (with either modified-live or killed vaccines) cannot keep a cattle herd free of BVD-PI cattle nor completely control BVD infection according to the Academy of Veterinary Consultants and American Association of Bovine Practitioners. Both groups promote a three-pronged approach to BVD control, a combination of BVD-PI testing and removal, vaccination and biosecurity.

Can I identify BVD-PI without laboratory testing?
Approximately 50% of BVD-PI calves are sick “poor-doers” that die before 1 year of age. However, the other 50% of BVD-PI cattle appear healthy as calves, grow normally and enter breeding herds or feedlots unnoticed. Despite looking healthy these subclinical BVD-PI animals still shed high levels of BVD virus and require laboratory testing to identify.

How do I get BVD virus out of my cattle herd.
Current recommendations from the Academy of Veterinary Consultants and American Association of Bovine Practitioners for control of BVD virus infection in cattle herds focus on identification and removal of BVD-PI animals. Control measures should include:

Diagnosis and removal of BVD-PI cattle
Vaccination to reduce BVD infection rate (Vaccination will not eliminate BVD virus from cattle herds)
Biosecurity to prevent introduction of BVD-PI animals

What testing strategy should be used?
Testing for BVD-PI cattle is different than testing for many other diseases because PI status stays the same throughout the animal’s life. Thus, BVD-PI testing is usually done only once. A BVD-PI test may be repeated to confirm a positive (since current laboratory testing by antigen-ELISA or IHC has a small percentage of false positive results)

Meet with your veterinarian to determine your BVD goals and exposure risk. Various testing strategies for whole herd testing exist. Below is a common example.

1. Prior to start of breeding season, test all calves and non-pregnant females without calves. Isolate pregnant females until they calve and test their calves.
2. Prior to start of breeding season, test all bulls and replacement heifers not previously tested for BVD-PI status.
3. Maintain documentation of BVD-PI test results.

What do I do with a positive BVD-PI test result?
Quarantine animal until second confirmatory test is run (BVD-PI “specific” laboratory tests, such at antigen-ELISA and IHC, have a low (approximately 2%) false positive rate). A second ear notch sample taken 2-3 weeks after the initial test will ensure whether or not the BVDV infection is persistent.

Ethically deal with confirmed BVD-PI animal by euthanizing animal, selling animal to slaughter, or sending animals to feedlot that feeds BVD-PI cattle. Don’t sell your problem to someone else.

Mother of BVD-PI calf should be tested for BVD-PI status. There is a small chance (approximately 10%) that the cow is also BVD-PI. Cows with BVD-PI calves that are not BVD-PI need not be culled. Remember, a negative BVD-PI animal is negative BVD-PI for life.

How do I prevent BVD virus from re-entering my cattle herd?
The following management procedures could reduce re-introduction of BVD virus into a typical cattle herd.

Maintain closed herd (not always practical)
Don’t purchase replacements from auction
Buy certified free or BVD PI tested livestock
Quarantine new arrivals and show stock for 30 days and test new arrivals for BVD PI
Test purchased pregnant animal and its calf at birth
Keep records (reproduction and health)
Address health problems
Determine why cows abort, why calves are sick, and why animals die

Contacts at Washington State University for Consultation / Advice / Interpretation of Test Results