BVD stands for bovine viral diarrhea.

Despite its name, BVD is not just diarrhea, it is a group of diseases caused by the BVD virus. It gets confusing because some people use the word "BVD" to refer to the virus itself.

The BVD virus causes different diseases depending on what animal is infected. The BVD virus can cause many different diseases because it damages the immunity of the cattle it infects.

In feedlot calves. BVD usually shows up as pneumonia (BRD) or undifferentiated fever (UF). Sometimes BVD causes diarrhea too, but that isn't very common.

In suckling beef calves, BVD can cause diarrhea or pneumonia. It can cause calves to be unthrifty without other signs of illness other than "not doing well". Research in Saskatoon shows that calves born in cow herds where there is BVD, tend to have lower weaning weights than in cow herds without BVD.

In pregnant cows or heifers, BVD can make the cow or heifer have a fever, but the biggest problem is that BVD can infect the unborn calf. If it infects the unborn calf, it can kill it leading to cows that are open or can cause outright abortion.

If the unborn calf is infected late in pregnancy, it can be stillborn. Sometimes BVD doesn't outright kill the unborn calf. In this case, the calf will be born stunted or weak. If BVD infects the unborn calf in the first 5 months of pregnancy and doesn't kill it, the calf may be born and be a carrier of BVD. See What is Persistent Infection.

In bulls, BVD virus may cause mild sickness, as it does in cows. Most of the time, you wouldn't be able to tell that it was BVD that caused the bull to get sick. The big problem for bulls is that BVD can infect their testicles. If it does infect the bull's testicles, the bull will have BVD virus in its semen for weeks to months after it recovers from the BVD infection.

When a pregnant cow is infected in the first 5 months of pregnancy, her unborn calf may become infected with the virus and be born a carrier. These carriers, called PI's, will be infected with BVD virus for their entire life. They spread the BVD virus to other cattle that they contact. If they are sold into a feedlot, they will spread the BVD virus throughout the pen.

These carriers tend to die before they are 2 years old but they can survive for years. If a heifer calf is born a carrier and she is kept as a replacement, she will always give birth to carrier calves.

Carriers often die young, but it isn't often clear that they have BVD. You need a lab test to find out for sure if they are carriers. The easiest test uses a bit of skin like an ear notch for the test. See What is Persistent Infection.

How you control it depends on what type of beef operation you have:

In cow herds, the goal is to make sure that you protect the pregnant cows. You need to make sure that the cows and heifers are vaccinated with an approved BVD vaccine before they are bred. The vaccine should have both type 1 and type 2 BVD viruses in it. Vaccinating before breeding makes sure that the unborn calves are not infected in the first 5 months of pregnancy so they don't become carriers. Cows and heifers will need a booster every year before breeding. The bulls should be vaccinated too, to protect them from getting infection in their testicles.

In seed stock cow herds, you can test for carriers and remove them making the herd "BVD carrier-free". Even if you do that, you still need to protect the breeding herd to make sure new carriers aren't formed. You also need to make sure you keep BVD out of the herd.

In the feedlot, you need to make sure that calves are vaccinated against BVD. That way they will be protected if a carrier ends up in their pen. Ideally, calves should be fully vaccinated before they go through the sale process rather than on arrival at the feed yard.

Now people are testing calves on arrival at feed yards to see if they are carriers. The idea is to find and remove these carriers before they spread BVD throughout the pen or into the pens on either side.

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