Expose the myths of BVD

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Getting rid of a healthy-looking calf is difficult. Scott Smith, veterinarian with The Dairy Authority in Greeley, Colo., has had to broach the topic with clients when their calves test positive for bovine viral diarrhea (BVD). On a couple of occasions, the clients wanted to raise the calves further, so they could butcher them for meat. One calf made it four months before dying; another made it six months. 

In many cases, “they can look just fine when they are born, but within three to four months are sick and don’t respond to treatment,” Smith says.

A popular misconception is that BVD-infected calves are always thin, with rough hair coats. But they can look perfectly fine. And, “it’s always tough for (producers) to get rid of what seems like a healthy animal,” Smith says.

When it comes to BVD, don’t fall prey to the following misconceptions.

1. BVD won’t affect my herd if I vaccinate.

“The vaccines are good, but they are not perfect,” Jeremy Schefers, lead pathologist for dairy cattle at the University of Minnesota Veterinary Diagnostic Laboratory, told those attending the recent Minnesota Dairy Health Conference.

Vaccination alone will not solve BVD, he said.

That assessment is shared by Julia Ridpath, lead scientist for the BVD project at the Agricultural Research Service’s National Animal Disease Center in Ames, Iowa.

To illustrate her point, Ridpath makes an analogy to seat belts. Just because a person uses seat belts doesn’t mean he can drive worry-free. That person still needs to practice defensive-driving techniques. The same applies to vaccines. Like seat belts, they can reduce the impact if you have an accident, but they won’t necessarily prevent the accident from happening in the first place.

You can have 99 percent of your animals BVD-free, but that one persistently infected (PI) animal in the herd will continue to shed the virus and expose other animals. Enough virus may be shed that it overwhelms the protective nature of the vaccine. That’s why it’s so important to test your herd and get rid of PI animals. 

“Vaccines are an adjunct to good management,” says Tom Shelton, senior technical services specialist for Intervet. “It’s a mistake to rely on vaccines to compensate for poor management.”

2. BVD will always cause obvious clinical signs.

Some producers swear they don’t have a BVD problem. They are not seeing obvious clinical signs, such as bloody diarrhea or a rise in abortions, and their animals look pretty good.    

“I’ve seen this on a number of occasions on small operations where there are not a lot of animals moving in and out of the herd,” Ridpath says. Despite longstanding BVD problems, things have settled down. The fact there are still a few PI animals in the herd may not become obvious until those animals leave the herd or new animals come in.

How an animal responds to BVD depends on a number of things, including her immune status and the strain of BVD involved. An animal exposed to a highly virulent strain of BVD can survive and possibly avoid clinical signs if she has even a low-level immune response (manifested by an antibody titer level of 1:16), Ridpath says.    

Naïve animals with little or no built-in immunity will be much more susceptible to the devastating effects of BVD.

3. Persistently infected calves will always be thin, have rough hair coats and be poor-doers.

That is not always the case. A lot of PI calves look completely normal, Schefers says. A lot of them do very well. 

You have to test (using tissue samples) to confirm health status — it is not a visual thing, Ridpath says. 

4. Calves are PI because their dams are PI.

Only a small percentage of dams are PI. In most cases, a cow that gives birth to a PI calf has been exposed to BVD during pregnancy. Since she was infected later in life — and wasn’t born that way — the cow is not PI. But her calf will be PI if infected in utero during the early part of gestation.



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