BVD disease is one of the most complicated viral diseases in dairy cattle worldwide. Terms associated with BVD such as “cytopathic” vs. “noncytopathic”, “persistent infection” vs. “transient infection”, “types I and II” and “immunosuppression” make understanding this virus a difficult task. However, the results of this disease are very clear-economic losses due to poor performance, loss of milk production, open cows, abortions, calf sickness and death. In order to control this problem, producers must first know if the virus is circulating in their herd. If so, then efforts must be focused on finding those infected individuals, minimizing their harmful effects and eliminating them from the herd at the right time. If the herd is free of BVD virus, then it is of the utmost importance to keep the virus out and minimize losses if it is accidentally introduced.
A basic understanding of the disease is essential to finding the appropriate strategy for your farm. The virus is picked up by a cow or calf by breathing it in (inhalation) or swallowing (ingesting) the organism. The virus can survive in the environment up to 7 days and may be brought in on trucks, tractors, boots, or gloves or carried in by wild animals. It can also travel in the air, including across fences from a neighboring farm. However the most important source of the virus is a cow or calf already infected with BVD. Once exposed, what happens next depends on the immune system of the cow or calf (vaccination status), aggressiveness (“virulence”) of that strain of virus, and the overall stress level present in the herd. Symptoms of disease range from a mild fever to severe diarrhea and death.
Clinical signs of acute BVD (also known as “Transient” or “Primary” BVD) disease in young dairy animals 3-12 months old may include:
• Unthrifty/Rough hair coat (calf looks “wormy”)
• Ulcers in the mouth (slobbering)
• Hemorrhage (bleeding) and death
Perhaps the most important symptom of BVD virus in calves is one we cannot see-immunosuppression. The virus actually keeps the calf’s immune system from functioning properly so other infectious diseases such as pneumonia and calf scours are much more severe and often lead to death.
Clinical signs in dairy cows are generally mild and seldom noticed but the infection causes serious consequences if it occurs during breeding season or early pregnancy (1st and 2nd trimesters). Reproductive effects of the BVD virus include:
• Failure to Conceive
• Early Embryonic Loss (Long time to return to heat)
• Abortion (up to 6 months)
• Mummified Fetuses
• Developmental Defects or “Dummy Calves”
• Calves with eye defects such as cataracts and retinal degeneration
• From 180 days on, a normal calf is produced.