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Veterinarian View | March 2024

What is Persistent BVD?

contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,

Rockwell City, Iowa



As the spring bull sale season starts, I have been asked about BVD several times. Many of the sales are advertising that all bulls have been tested negative for BVD. One client was asking me if that is something he needed to be doing for his herd. What these herds are testing for is persistent (PI) BVD infection, which is different from just an infection from BVD.


BVD Natural Infection

When a feeder calf becomes infected with BVD, this is a natural infection from BVD circulating within the herd. When we vaccinate with a 5-way modified live viral vaccine in our preconditioning programs, this is the type of infection we are trying to prevent. If the calf does become infected, it will build an immune response to fight off the infection and clear the virus from its system. So, any animal that is fed out or sold as breeding stock has the potential to have picked up this type of BVD infection and cleared it. This is not the type of BVD that is typically tested for when someone advertises as tested BVD negative.


Persistent BVD

Persistent BVD (PI-BVD) infection is what we typically test for when someone wants to advertise as BVD negative. Also, some of the major winter cattle shows want cattle to have a negative BVD test to enter the show and this PI-BVD is what we would be testing for.


PI-BVD infection is when a calf is born with the infection. In this scenario, the calf is infected while it is still a fetus in the uterus. When this happens the developing fetus’s immune system does not recognize the infection as a foreign invader to their system. This allows the viral infection to persist after the calf is born.


The calf will be infected with BVD for the rest of its natural life because the calf’s immune system never does recognize the BVD virus as an infection. This results in the calf essentially being a Typhoid Mary, but instead, persistently shedding BVD in the environment.


Prevention

So how do you prevent this from happening? The first thing is to make sure that the cow is properly vaccinated for BVD before the breeding season and continues to get an annual booster. This needs to be done with a product that is labeled for fetal protection from BVD. There are many products that have this claim, so it is best to work closely with your herd veterinarian to be sure that you are using the right type of vaccine for your herd.


BVD Case

Probably the worst case of PI-BVD I have ever diagnosed was in a herd that was procuring infected bottle calves through a cattle trader to foster onto cows that had lost their calves. In this case, the owner had been using a lot of different treatments on nursing calves for respiratory infections with very poor response.


I looked over his diagnostic lab reports and the only thing they had not checked for was PI-BVD. We tested 30 calves out of 130 head and found a 25 percent infection rate in those 30 calves. We immediately vaccinated all the cows with BVD vaccine that had a fetal protection label. The other thing we did is early wean the calves to an offsite premise to prevent exposure to the pregnant cows from the infected calves.


The next year, he tested 100 percent of his calves and only had two out of 130 head. These were probably calves that had been infected as fetuses before he weaned the calves and vaccinated the cows. He has continued to test 100 percent of his calves each year and has been free of PI-BVD ever since. This is an extreme case, and we typically only find one in a group. The reason that the major shows want proof of a negative PI-BVD test is to prevent the transmission of BVD to pregnant females that may be at the show.


Testing

If someone wants to test their herd, I recommend that they test the entire calf crop. If a calf comes back as negative, it means the dam is automatically negative. This is because any PI-BVD positive females will automatically transmit this to their offspring. Thus, by testing the offspring you automatically are testing the cow herd, and the progeny are also tested negative for any marketing plans or biosecurity reasons.


If a calf would happen to test positive, you will want to test the dam. While a positive dam always results in a positive calf, a positive calf can come from a positive or negative dam. If a negative cow is exposed to a regular BVD infection, she will clear the virus herself, but if she is pregnant, the calf may become persistently infected. If a negative cow gives birth to a positive calf, this does not mean she will always have a positive calf in the future. By using a BVD vaccine in the cows with a fetal protection label, you can prevent the fetus from being infected in this scenario.


For testing, we typically will use an ear notch preserved in formalin. The lab will run an immunohistochemistry test on this sample. To be accurate, the test needs to be run within seven days of being collected. The other way is to run a capture ELISA test on a serum sample. The ear notch is a cheaper test, but for show animals, we typically run the serum capture ELISA test. We also will use the serum test if we are drawing blood for other testing, such as screening recipients for a panel of diseases.


BVD Signs

In school, you will learn that PI-BVD calves will be unthrifty and rarely make it to adulthood. If they do, they will typically be poor doing. I can tell you from experience that if an animal makes it to adulthood, they will be hard to identify from any of their healthy negative herd mates. Even infected calves will be hard to identify based on if they look unthrifty or not.


While I wrote about an extreme case in this article, rest assured that PI-BVD is actually rare to see. But when it shows up, it can cause a multitude of herd health issues. PI-BVD is a complex disease, so work closely with your veterinarian to develop a vaccine program and a biosecurity protocol that works best for your herd so as not to be affected by it.



Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.

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