BVDV Control in Dairy Herds

Bovine viral diarrhea virus, or BVDV, can cut fertility, cause abortions and weaken calves. Control comes down to finding and removing the animals that spread it and keeping new virus out.

Key points

BVDV causes hidden losses in fertility, calf health and immunity.
Persistently infected animals are the main source of spread.
Testing, quarantine and biosecurity do most of the work.
Vaccination is one layer, not a replacement for removing PI animals.
Work out a written herd plan with your vet.

What BVDV is and why it spreads

BVDV is a virus that affects cattle in several ways. It can cause fever, diarrhea and reduced milk, but often it causes quiet losses: poor conception, early embryo loss, abortions, weak calves and more respiratory disease because the immune system is suppressed.

The virus spreads through nasal discharge, manure, milk, semen and contaminated equipment. The biggest source of spread in a herd is a particular kind of animal, described next.

Because losses are often quiet, many herds learn about BVDV only after they notice poor reproduction numbers or a run of weak calves. Looking at your reproductive records is a good first step.

Persistently infected animals

A calf infected in the womb at a certain stage of pregnancy can be born persistently infected, called a PI animal. The calf never clears the virus and sheds large amounts throughout its life. A PI calf may look normal, or may be small and unthrifty.

Because a PI animal sheds virus all the time, finding and removing PI animals is the core of most control programs. Your vet decides the testing steps and what to do with positive animals.

Testing options

Several tests exist. Some work on blood, some on tissue samples taken at ear-tagging, and some on bulk tank or pooled milk samples to screen herds. Ask your vet which fits your herd and how to read results, including cases where a retest is needed.

A calf that tests positive once may not be a true PI animal, so follow your vet's confirmation steps before decisions are made.

Testing is most useful when it follows a clear plan. Decide before sampling what you will do with a positive result, and who will carry it out.

Test new arrivals before they mix with the herd
Test calves born to cows that may have been exposed
Ask about herd screening using milk samples
Test dams of any PI calf found
Keep every result in your records

Biosecurity

Keep virus out. Quarantine and test purchased cattle, including animals returning from shows or other farms. Be careful with pregnant animals, since a purchased pregnant cow may carry a PI calf even if the cow itself tests clean.

Limit nose-to-nose contact over fences with neighbors' cattle. Clean and disinfect trailers and shared equipment. Ask visitors to wear clean boots and clothing.

Vaccination as one layer

Vaccination can reduce the effect of the virus and protect against fetal infection, but it does not replace testing and biosecurity. Timing matters, particularly before breeding. Ask your vet to match products and timing to your herd, and read the label for pregnancy restrictions.

Treat vaccination as one layer of a program that also includes testing, removal of PI animals and herd closure where possible.

Remember that fencing, shared pastures and the movement of cattle through sale barns all raise exposure, so think about where your animals meet others.

Signs that should trigger a call

Unexplained abortions, repeat breeders, weak or deformed calves, ongoing scours or pneumonia in young stock, and cattle with oral lesions or severe diarrhea all justify a conversation with your vet. Collect samples as your vet directs rather than discarding aborted fetuses or tissues.

Clusters of abortions
Poor conception without another reason
Calves that fail to thrive
Outbreaks of respiratory disease in young stock

Records and next steps

Keep a file for each animal tested, with date, test type and result. Record purchases, quarantine dates and vaccine events. A herd plan written with your vet, and reviewed every year, keeps the program working even when staff change.

When to get help: Call your vet about unexplained abortions, weak calves or a positive test, and follow their testing and removal steps. Any animal treated for related illness must be held for the full label or vet-set milk and meat withdrawal time.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

More in Herd Health & Disease Management

← Vaccination Schedules for Dairy Herds Johne’s Disease: Testing, Culling, and Biosecurity →