There is no effective treatment that can alter the course of BVD infections, but most BVD virus infections are subclinical and self-limiting. If treatment is initiated, antibiotics, B vitamins, and fluids may be used in attempts to control secondary infections and provide supportive therapy. Changes in feed rations to enhance the palatability of the feed could tempt the sick animal to eat needed nutrients.
Vaccination of susceptible cattle has been the principal approach to the prevention and control of BVD. Presently, there are two forms of BVD vaccine:
Replicating BVD Vaccine
Modified Live Virus (MLV) Vaccine - usually requires only one injection to stimulate long protection. Modified live BVD vaccines should not be administered to pregnant cattle during any stage of pregnancy. If the cattle are in the first 120 days of pregnancy, the fetus may become infected with the vaccine virus and be aborted, be born weak, or be born in apparent good health but be persistently infected. Such calves never develop a measurable antibody titer and can be a lifetime shedder of the virus. If later exposed to a different BVD virus, they may develop mucosal BVD disease and die. If cattle are in the last half of pregnancy when vaccinated with a MLV, the fetus may become infected, die and be aborted.
Most MLV-BVD vaccines can be administered to calves nursing pregnant cows. The MLV-BVD vaccine virus is non-shedding and should not be transmitted to the pregnant cow. Read the label! The misunderstanding about the vaccine's use in calves nursing pregnant cows is due to combination vaccines. Most MLV BVD vaccines are in combination with a replicating MLV IBR vaccine. Replicating MLV IBR vaccines should not be used in calves nursing pregnant cows; the IBR virus may shed from the calves to the cows and cause abortion. However, young calves that nurse BVD-vaccinated cows will possess materinal antibodies that can neutralize the MLV-BVD vaccine administered to the calves. Hence, most labels on MLV-BVD vaccine advise users that animals vaccinated before 6 months of age should be revaccinated at 6 months of age.
Non-Replicating BVD Vaccine
Killed Virus vaccines are safe to use in all cattle regardless of the pregnancy status. It requires two doses of killed virus vaccine to initiate a high level of resistance. It also requires that the animal receive a minimum of one annual booster to maintain a significant level of resistance.
There has been a lot of discussion about MLV-BVD vaccines causing problems in cattle, especially newly arrived feedlot cattle. Remember, if the animal has already been exposed and is incubating the BVD disease virus, vaccination will not alter the disease course. You could vaccinate an animal incubating the disease and when it broke with BVD, the vaccine would be erroneously blamed. Some researchers have suggested that if a persistently BVD-infected animal was vaccinated with a MLV-BVD vaccine, the animal could come down with the mucosal form of BVD. What they fail to say is "essentially there is no way to adequately protect a persistently BVD-infected animal in a BVD-infected herd." Detection of the persistently infected animals requires special virus identification tests that are available to be run at several diagnostic laboratories in the U.S. Vaccines do not protect infected animals; vaccines aid in the prevention of infection.
Most outbreaks of BVD have occurred in herds with a history of no or inadequate BVD vaccination. A single initial dose of a killed BVD vaccine is inadequate even if boostered annually; the second dose of the initial vaccination protocol must be administered for adequate vaccination to occur. While adequate vaccination appears to protect the cow from severe disease, it may not always protect the fetus. Most current vaccines contain Type 1 BVD virus, but there appears to be some cross-protection against Type 2 BVD virus, at least for a short period. If your herd is at risk of developing BVD, then it would be advisable to make sure the herd is adequately vaccinated. We now have BVD vaccines which contain both Type 1 and Type 2 BVD antigens.
If the herd in question consists of pregnant animals, you must use a killed form of the vaccine. If you suspect a Type 2 BVD challenge, then it would be advisable to use a killed vaccine containing Type 1 and Type 2 viruses, or to administer booster vaccines at three-month intervals with different killed-BVD vaccines (switch companies every three months).
If the animals are not pregnant you could use a MLV-BVD vaccine. There also appears to be more cross protection against Type 2 BVD viruses when using MLV-BVD vaccine than when using the killed forms. Several manufacturers have provided the industry with MLV-BVD vaccines containing both Type 1 and 2 BVD viruses.
To control and prevent BVD infections, it is important to establish an immune population before a disease appears. A few basic principles can provide a framework on which to build a BVD vaccination program:
1. Initiate vaccination of calves after 4-6 months of age to avoid interference from maternal antibodies passed to the calf during colostral feeding. When using killed BVD vaccine, re-vaccination in 30-60 days will be required to stimulate an adequate level of protection. The BVD vaccinations should be completed in the calves at least 30 days before weaning.
2. Properly vaccinate all unvaccinated heifers and cows before breeding to ensure protection for the fetus.
3. Properly vaccinate all bulls before putting them out with the cows or heifers.
4. Properly vaccinate all new additions before adding them to the herd.
5. When using killed BVD vaccine, annual boosters are required to maintain an adequate resistance level when dealing with Type 1 BVD. If dealing with Type 2 BVD, vaccinate using a killed BVD vaccine containing Type 1 and Type 2 viruses or booster at three month intervals using different company products. Breeding stock should be booster vaccinated immediately before the breeding season to provide maximum protection to the fetus. Even if MLV-BVD vaccine was used as the initial vaccination agent, a booster vaccination using either MLV or killed BVD vaccine is recommended every few years. Remember, do not booster vaccinate pregnant cows with replicating BVD vaccine.
Even the best vaccines cannot always overcome poor health, poor immune status, poor timing of vaccine administration, overwhelming disease challenge, or virus strains divergent from the one the animal has been vaccinated with.
Dr. Kenny Brock at Auburn University has initiated the Top 10 List to prevent BVD in a herd. It is as follows:
1. Maintain a strict level of herd biosecurity.
2. Purchase only open animals that are known to be BVD-negative before purchase.
3. Isolate any new additions or animals re-entering the herd for a minimum of 30 days.
4. Test any new additions for BVD, and vaccinate during the isolation period.
5. Maintain good sanitation and routinely disinfect contaminated areas. Prevent contamination from outside sources by disinfection.
6. Prevent contact with neighboring cattle of unknown status.
7. Protect pregnant animals from potential sources of exposure during the first trimester.
8. Prevent mixing of animal groups immediately before breeding and during the first trimester.
9. Conduct surveillance for BVD by performing necropsy on dead animals and collect blood samples on any calves that are poor-doers and calves that have respiratory disease.
10. Vaccinate the cow herd yearly. Ensure that heifers are properly vaccinated at 6 months of age (two doses) and are booster vaccinated before breeding.
Source: E. J. Richey, DVM, University of Florida Extension