Don’t let the ‘Trojan dam’ bring BVDV into your herd

Control and prevention of bovine viral diarrhea virus (BVDV) in the herd requires a three-pronged attack with biosecurity, testing and immunization.

3 Min Read

Bovine viral diarrhea virus (BVDV) continues to be a vexing problem for cow/calf producers. BVDV is spread in multiple ways, and the risk-control effort needs to have a multipronged approach.

According to Dr. Paul Walz, professor of pathology at Auburn University, there are three steps to controlling BVDV infections:

  • Biosecurity

  • Immunization

  • Testing


A persistently infected (PI) cow will always have a PI calf. Walz points out the PI calf is a central figure in how BVDV maintains itself within a herd and how BVDV travels from herd to herd. But the risk for spreading BVDV extends throughout an operation, to equipment, visitors to the farm and fence-line contact among animals. A strong biosecurity plan is critical.

The main path for BVDV introduction to a herd is through new cattle. The “Trojan dam” — a highly immune cow that is a PI carrier in its reproductive tract and uterus — makes detection difficult, explained Walz. The cow would pass any test for BVDV, but it is an infected animal. Producers who purchase pregnant animals, or are bringing them back from a heifer raiser, must contain them separately from the rest of the herd for biosecurity purposes to reduce BVDV spread.

“If at all possible, test for PI status of the newborn calves on the new cows rather than allowing those cows to calve within the general population,” Walz said.

Walz shared some other essential components of effective biosecurity measures:

  • Avoid bringing in new animals unless they’ve been tested.

  • Isolate sick animals from healthy ones.

  • Move dead animals away from the barn.

  • Pay special attention to young animals.

  • Practice general hygiene — soap, water and general disinfection.

  • Monitor visitors and be aware of how they can transmit BVDV from farm to farm.


Vaccinating is the act of giving the animal a vaccine, explains Walz, while immunization is when the animal has an immune response to the vaccine. He said ideally producers will give two doses of modified-live virus reproductive vaccine in replacement heifers before they are bred for the first time, with the last dose given at least 30 days prior to breeding.

Annual revaccination with a modified-live virus vaccine, like Bovi-Shield Gold FP® 5 VL5, gives the best protection against BVDV infections. If a modified-live virus program in the mature cowherd doesn’t work for the operation, a killed BVDV reproductive vaccine, like CattleMaster Gold FP® 5, at pregnancy check time can also provide good protection for the herd against BVDV infection.

“We cannot rely on immunization to 100% prevent PI infections, nor can we look at our diagnostic test to pick up every single PI animal, so that’s why biosecurity is a really good way to reduce risk,” Walz said.

The importance of BVDV testing

“We have excellent tests available for BVDV,” Walz said. “We have better tests for BVDV than we have for a lot of our other diseases, including infectious bovine rhinotracheitis.”

Walz said testing the newborn calf is essentially testing the dam since a negative test on the calf confirms the dam is negative. However, a calf with a positive test can be born of a dam that is positive or negative for BVDV, so further testing of the dam is required. Knowing those results can set in motion biosecurity measures and other steps. There are numerous ways to test and working with a diagnostic laboratory can help produce the most useful results.

“Your diagnostic lab is a tremendous resource for testing, but also a tremendous resource for information on how to test and when to test,” Walz said.

For more information on biosecurity and taking steps to reduce the risk of BVDV, work with your local veterinarian, or visit to learn about vaccine options from Zoetis to help protect the cow and unborn calf.



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