BVDV Control in Ranch Herds

Bovine viral diarrhea virus, or BVDV, can quietly cost a herd through open cows, abortions, and sick calves. The key to control is finding and removing the animals that spread it.

Key points

BVDV causes fertility, respiratory, and calf health problems.
Persistently infected animals are the main source of virus.
Testing finds PI calves, and removal stops spread.
Vaccination helps but does not replace testing and biosecurity.
Quarantine and check purchased animals, especially bred females.

What BVDV does

BVDV is a virus that can cause many problems, including fever, respiratory disease, diarrhea, poor fertility, abortions, and weak or deformed calves. It also weakens the immune system, making other diseases worse.

Because the signs vary and often look like other illnesses, BVDV is easy to miss. It is often the hidden cause behind herd health problems.

Because the virus weakens the immune system, a herd with BVDV may see more pneumonia and scours than similar herds, even when the standard vaccine and handling steps are in place.

The role of persistently infected animals

The most important source of virus in a herd is the persistently infected animal, often called a PI. A PI calf is infected before birth, when its dam is exposed during early pregnancy, and the calf can never clear the virus. It sheds large amounts of virus for life.

Some PI calves look fine, while others are small and unthrifty. A PI can spread the virus to every animal it contacts, which is why finding them matters so much.

A cow that is exposed to the virus at the wrong stage of pregnancy may look perfectly healthy and still carry a calf that becomes a PI, so a quiet herd does not mean a clean one.

Infected before birth, carries virus for life
Sheds virus to herd-mates
May look normal or may be unthrifty
Dam may not show signs during pregnancy
A PI cow will always have a PI calf

How it spreads

Virus moves by direct contact, nose-to-nose over fences, shared water, and contaminated equipment. Purchased cattle, especially pregnant cows and heifers, can bring in a PI calf in the womb, even if the cow looks healthy.

Fence-line contact with neighbors' cattle and commingling at fairs, shows, and sales are also risks. See our biosecurity and quarantine guides for steps to reduce exposure.

Wildlife, other livestock, and cattle from many sources can add complexity. Ask your vet which exposures matter most on your place.

Testing and finding PI animals

Your vet can arrange testing to find PI animals, often at calving or at birth by sampling tissue such as an ear notch. Testing calves early lets you remove PIs before they spread virus.

Ask your vet about the right testing plan for your herd, how to deal with positive results, and how to interpret retests. Testing decisions should follow veterinary guidance.

Test results should be handled by your vet, who can explain how to keep the PI calf separated and how the dam should be treated while a final decision is made.

Vaccination

Vaccination is one part of control. The timing, product type, and safety for pregnant cattle differ, and the choice depends on your herd. Talk with your vet about a vaccine plan that fits your breeding and calving schedule and your cattle.

Vaccination does not replace testing and biosecurity. A vaccine can lower risk, but it does not remove a PI animal from the herd.

Read the label for limits on pregnant cows, and ask your vet about timing before breeding so that fetal protection is part of the plan.

Biosecurity and purchases

Quarantine all new cattle, and ask your vet about testing purchased animals. Be especially careful with bred females, since the calf in the womb could be a PI. Ask about the dam and the calf at side when you buy a pair.

Limit contact with other herds across fences and avoid sharing equipment without cleaning it.

Keep a written plan for visitors and equipment, and review it with your vet each year, especially if you buy cattle regularly.

Records and common mistakes

Keep records of testing, calving, losses, and purchases. Patterns in abortions, open cows, or sick calves can help your vet decide whether BVDV is involved. Write down the dam of every calf and track calves that fail to thrive.

Common mistakes include keeping a PI calf because it looks healthy, relying only on vaccination, buying bred cattle without checking, and skipping testing. Treat any unthrifty calf as a reason to ask your vet. Follow label directions and withdrawal times on any product used.

When to get help: Work with your veterinarian on a BVDV plan that covers testing, vaccination timing, and purchases. Follow label directions and withdrawal times for any product given to cattle.

Sources and further reading

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

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