Bovine viral diarrhea (BVD) virus can cause several medical issues, such as intestinal destruction, pneumonia, abortions, calf deformities, and general compromise to the affected animals’ immune system. The virus most often targets animals between the ages of 6 and 24 months. The virus may take a highly pathogenic course of action, or remain in a somewhat latent or persistent infection mode. Animals may become infected through placenta transfer or direct contact with feces, milk, semen, or nasal discharge of an affected herd mate.
Animals with persistent infections are considered to be the natural reservoir for the virus in the environment. Persistent infection develops when the virus is spread through the placenta during the first four months of fetal development. The calf can be born with natural immunity to the virus, yet shed virus particles to those less fortunate in the same herd.
Calves infected through the dam’s placenta after approximately four months of gestation are more likely to be born deformed or aborted. Cows that are not well vaccinated are most likely to create calves developing persistent infections. In addition, cows with persistent infections will always have calves with similar circumstances.
Clinical signs may appear vague in beginning stages of infection. Calves will often demonstrate fever, nasal discharge, diarrhea, and inappetence. Mucosal ulcers may or may not accompany disease. The mucosal disease component is a highly fatal form of disease and is rarely found in cattle with persistent infection.
The most commonly encountered birth defect associated with BVD is cerebellar hypoplasia, also described as the inadequate formation of the cerebellar portion of the brain. Calves will demonstrate difficulty with regular movement, muscle tremors, and decreased ability to nurse appropriately for nutritional needs.
Routine testing of your herd is important in managing potential persistent infections, especially if animals have been brought into the herd from unknown status sources. The preferred method of analysis is via immunohistochemistry of skin samples or ear notches. Your veterinarian will send the collected samples to an appropriate laboratory for evaluation. All animals should be tested—versus just clinically ill ones—in order to assess for a persistent infection present in the herd.
Calves found to be persistently infected with BVD should be euthanized in order to prevent further chance of virus exposure to other animals in the herd.
Economically, this may not seem feasible to many producers, but one must think more along the lines of long term consequences when keeping infected calves around the farm. Infected calves should be quarantined from the rest of the herd, and their survival rate is very unpredictable at best.
It is possible to eradicate and prevent BVD from your herd with diligent work. Managers have succeeded in this effort by practicing strict biosecurity protocols, routine testing surveillance, and proper vaccination programs. Current vaccinations containing the modified live virus are recognized to be very efficient in preventing disease and may even last up to 18 months in duration of immunity.
Losses from affected animals arise due to severe diarrhea and respiratory disease, decreased weight gain, and increased susceptibility to concurrent diseases. According to research conducted by APHIS, losses may equate to a minimum of $400 per cow, depending on severity of disease within the herd.
Contact your herd veterinarian for more information, and to begin a BVD management protocol for your facility today. —
Dr. Genevieve Grammer
[Dr. Genevieve JM Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to drgigi19@ gmail.com