Bovine Viral Diarrhea (BVD)
Eleanor Jenson, D.V.M.
USU Extension Veterinarian
Bovine viral diarrhea (BVD) infections in cattle can cause a variety of clinical signs or they may cause subclinical infections that show no apparent signs. BVD may affect the digestive tract, causing diarrhea and weight loss. Animals may also develop a fever, respiratory disease, or systemic diseases, such as mucosal disease. The embryo or fetus can also become infected.
The economic impact of BVD can be significant in dairies affected with this viral disease. Costs may be incurred from medication and labor to treat acute infections. BVD causes milk production losses in lactating cows and infertility due to decreased conception and early embryonic death. It also causes abortions and weak, abnormal calves. Possibly the biggest cause for concern is persistently infected (PI) calves. These calves are infected in utero between days 58 and 125 after conception. During this time, the fetus does not recognize the virus as foreign, and therefore, does not develop an immune response against the virus. These persistently infected calves continually shed the virus in high numbers throughout their lives. Many of these calves are relatively healthy and show no clinical signs of BVD.
Efforts to control and prevent BVD infections should be directed at enhancing individual animal�s immunity by vaccination and reducing the risk of exposure to the virus. For herds where BVD is suspected, animals can be tested for those persistently infected by collecting a small piece of skin from the ear. An ear notcher is used and the skin sample is placed in buffered formalin, and submitted to the diagnostic lab for immunohistochemistry testing. The Utah Veterinary Diagnostic Laboratory located in Logan currently performs this special skin test for $5.00 per sample. Animals with positive results should be retested at least 30 days following the initial test to confirm persistently infected animals. All PI animals should be culled and sold only for slaughter.
When new animals are purchased they should be isolated from the existing animals and tested for BVD. This can be done using the skin test as described above. Persistently infected replacement animals should not be purchased.
Vaccines are essential aids in preventing BVD infections. Heifers should be vaccinated after 6 months of age and preferably again at 1-2 months prior to breeding with a modified live virus vaccine. It is important to vaccinate females prior to breeding to maximize the immune response during early gestation when the fetus is most at risk of becoming persistently infected.
Once BVD is eradicated from a herd, reinfection must be prevented by maintaining a routine vaccination program, and isolating and testing newly purchased animals. The effects of BVD on a dairy farm can be far reaching. This is a disease that should be addressed on all dairies by implementing effective eradication and control programs.