What is BVD?
Bovine viral diarrhea (BVD) is the name of a group of diseases in cattle all caused by the BVD virus.
What diseases does BVD virus cause?
BVD virus causes different diseases depending on which cattle it infects. The most severe problems occur when pregnant cows and heifers are infected. When this happens, the virus can cause breeding problems with irregular heats. Sometimes it causes abortion, premature births or the birth of weak or stunted calves. Sometimes calves are born which look healthy but are carriers of BVD virus. These calves will be carriers for the rest of their lives.
If the BVD virus infects calves, open heifers and open cows, it usually doesn't make these animals very sick. Even if an animal does not become sick from the BVD virus, the virus can temporarily damage the immune system. Infected animals are more likely to have other diseases like pneumonia. Most cattle recover from BVD but sometimes the infection is so severe that cattle will die. One type of severe disease is called acute BVD. Cattle with acute BVD go off feed, have a high fever and diarrhea. They may also have sores in their mouths.
What is mucosal disease?
Mucosal disease is one disease caused by BVD virus that occurs only under special circumstances. Cattle with mucosal disease have high fever, diarrhea that often contains blood and sores in the mouth. All cattle with mucosal disease will die from it, usually within a few days although some can live for weeks. Mucosal disease is special because only cattle that were infected with BVD virus before they were born will get it. Cattle that get mucosal disease are also carriers of BVD virus and have been carriers since they were born. These carriers are important in spreading BVD virus within and between farms.
Is BVD virus the only cause of these diseases?
Almost all the diseases caused by BVD virus also have other causes. Laboratory tests are needed to be sure that BVD is causing the problem. If BVD is suspected, it is important to select the correct samples to send to the laboratory to make the diagnosis.
Are all BVD viruses the same?
There are many strains of BVD virus. Most strains have not been assigned names. Each strain is a minor variation on BVD virus but all strains share similarities. The fact that almost all strains of BVD are similar means that vaccines made from one strain will provide protection against other strains of the virus.
How does BVD virus come onto a farm?
BVD virus is usually brought onto farms by carriers. BVD virus also can be brought onto a farm is by an animal that isn't a carrier but has recently become infected with the virus. These animals haven't had a chance to get sick or might not even get sick but will pass the virus to other cattle they contact.
What are carriers?
Carriers are cattle that were infected with BVD virus before they were born. They must have been infected in the first 125 to 150 days of pregnancy to be born a carrier. These cattle don't look sick when they are born but have BVD virus in their blood, nasal mucus, saliva, manure and urine. These carriers can live for years without becoming sick from BVD but most die of mucosal disease before they are 2 years old. Carriers are important because they pass the virus along to other cattle. Another way to describe these carriers is to say that they are persistently infected (PI).
How is BVD spread?
Once the BVD virus comes onto a farm, it usually spreads by contact between cattle. Generally, cattle must be close enough to have nose to nose contact to spread the virus. Because there is virus in nasal mucus and saliva, articles like unwashed feed pails or nipples can also spread the virus. BVD is also present in the urine and manure of infected calves and might also serve to spread the virus.
Does BVD virus cause long term contamination on a farm or in a shed?
Not likely, the BVD virus does not survive well away from cattle. Hog cholera, a virus that is very similar to BVD can only survive for about 2 weeks in faeces and dies more quickly in other fluids.
Can BVD be treated?
There is no cure for BVD but some animals will survive the infection. Treatment can be useful to reduce the impact of complications like pneumonia. There is no way to cure carriers, they will always be infected with the BVD virus.
If you have BVD in my herd, is there anything you can do to control the spread?
If you can, you should isolate animals with symptoms of BVD as well as any animals in direct contact with them. This will help limit spread to other cattle. You should handle infected cattle last. Be especially careful to handle pregnant cows and heifers before caring for sick animals. Cleaning and sanitizing may also help prevent spread.
Will you need to use special sanitation procedures against BVD?
The BVD virus is killed by disinfectants. Routine cleaning and power washing or disinfection will kill the BVD virus. Sanitation can be combined with an "all-in, all-out" to eradicate BVD in pens. Any new virus must be brought onto the farm by carriers or recently infected calves.
Will BVD virus infect humans or other animals?
BVD virus does not cause disease in humans. BVD virus can infect sheep and wild ruminants including white-tailed deer and bison.
How can herds protect themselves from BVD?
Producers can effectively increase the resistance of their herd and reduce the risk of exposing their herd to BVD.
Prevent the introduction of infected animals by:
- bringing in only animals from uninfected herds;
- bringing in only animals from herds with a known effective vaccination program;
- avoiding the purchase of animals from sales barns;
- testing new animals for persistent infection in advance of introduction; and
- isolating new animals for 30 days before allowing contact with animals on-farm.
Increase the resistance of the herd to BVD by:
- vaccinating strategically as directed by the herd veterinarian and the product label;
- maximizing colostrum consumption by newborn calves; and
- reducing stress on cattle caused by other diseases, poor nutrition, uncomfortable housing or poor air quality.
Decrease exposure to BVD by:
- preventing manure contamination of hair coat, feed and water;
- housing baby calves in individual calf hutches; and
- isolating sick animals.
Vaccination for BVD is an important component of a BVD prevention program.
What protection can you expect from BVD vaccines?
Vaccination does not provide complete protection against BVD. Vaccination will protect most cattle from becoming sick but some vaccinated cattle may get sick. When they do get sick, vaccination appears to protect them from getting so sick that they die. Vaccination provides some protection against infection of the fetus in pregnant cattle. Pregnant cattle may abort even if they are vaccinated but it appears that vaccination reduces number of cattle that will abort. Vaccinated cattle may still become infected with BVD virus and pass it to the other cattle even if they don't get sick themselves.
What should producers do after a BVD outbreak?
After an outbreak of BVD, producers must continue to be watchful to make sure that BVD does not become a chronic problem on the farm. Here are some points that producers should know about:
Your vaccination program is the best protection that you can give cattle against BVD. Cattle that have been infected with BVD do not have long lasting immunity. So it is important that producers all cattle and keep booster vaccinations up to date. Use vaccines according to the recommendations on the label unless your veterinarian makes different recommendations. Calves, heifers and cows that have not been vaccinated before will need a double vaccination the first time they are vaccinated with a killed vaccine.
Selling cattle from your herd:
There are no regulations to stop producers from selling cattle during an outbreak of BVD. To prevent the spread of BVD to other farms, we recommend that no cattle or calves should be sold other than to slaughter until at least 3 weeks after the last animal is seen to be sick. You may wish to advise prospective purchasers that an outbreak of BVD has occurred. We also recommend that if you sell heifers or cows that were pregnant during the outbreak, advise the buyer to test the calves when they are born to see if they are BVD carriers. If a calf is a carrier, it should be slaughtered.
Abortions after a BVD outbreak:
Producers who have outbreaks of BVD can expect abortions to occur several weeks after the last cattle are seen to be sick. The BVD virus can cause abortion by killing the fetus when pregnant cows or heifers are infected. The fetus is not expelled immediately after it dies. It often takes several weeks before the abortion occurs.
Carriers and BVD virus.
Any cows or heifers that were pregnant for less 5 months when they were infected with BVD virus may give birth to a calf that is a carrier of BVD virus. If these carrier calves stay in the herd you may have long term problems with BVD. We advise producers to test calves as they are born to identify any carriers.
The test to identify carriers is a blood test. You should arrange for testing through your veterinarian. Your veterinarian will help determine who should be tested. You should expect to start testing all calves born about 3 months after the date you saw the first animal sick from BVD. You should continue to test all calves until 9 months after the date you saw the last animal on your farm sick from BVD. Keep these calves away from pregnant cows and heifers until you know the result of the blood test.
There is no way to "cure" a carrier. Any calf that is a carrier when it is born, will always be a carrier. If you find that a calf is a carrier, we recommend that it be slaughtered. You should not sell a carrier other than to slaughter.
Bringing new cattle into your herd:
Even if you have vaccinated your herd, you should be cautious about bringing new cattle onto your farm. Try to arrange that purchased animals are vaccinated or boosted before they come to your farm. Vaccinated cattle are resistant to getting BVD, but they may still be able to carry BVD for a short time (from a few days to a few weeks) and can probably pass it to other cattle. This means that even vaccinated cattle could bring BVD (and other diseases) into your herd.
It is best to quarantine any new cattle by keeping them separate from your own cattle for about 3 weeks. To prevent spread of BVD, the quarantine pen should be located so your cattle cannot touch the quarantined animal. They should not share waters or feeders either. Be careful that manure is not transferred from pen to pen on feed or water buckets or manure forks.
After a BVD outbreak, the BVD virus can continue to cause disease problems. To reduce the chances of ongoing BVD problems, we recommend that producers maintain a good vaccination program. Producers should also test calves that are born after the outbreak to make sure that none are carriers that could keep BVD in the herd. Producers should always be cautious when selling or purchasing cattle.