About BVD and the advantages of establishing a BVD-PI Negative herd
About BVD and Persistently Infected (PI) Animals...
For cattlemen, the primary concern of spreading the BVD virus is through PI cattle; with transiently (or temporarily) infected cattle considered a less important source of the disease. PI animals are very efficient transmitters of the virus. They usually have a very high and virulent amount of virus circulating in their blood and other fluids; and they shed the BVD virus continually. A PI calf is "created" during pregnancy when BVD virus from an infected dam's bloodstream crosses the placental wall to her fetus during the first part of gestation. This is the only way a PI animal is created.
Fetal infection can lead to fetal death, the birth of a PI calf, or the birth of a normal calf. It's important to note that a calf born BVD-PI will always be a PI animal. If a calf is not PI at birth, it can never become PI. While uncommon, PI calves can grow to adult age without any outward signs of BVD virus infection. The virus is perpetuated when these PI animals - bulls or heifers - survive past yearling age and enter the breeding herd. PI heifers or cows that conceive will always produce a PI calf. A PI bull has the dangerous potential to effectively and efficiently spread the BVD virus to all cattle with which he comes into contact.
Immunizing cattle herds with appropriate vaccines to protect against transient infection should be the first consideration in a herd biosecurity program. But, given the right conditions, the tremendous amount of virus secreted by a PI calf can overwhelm a level of immunity provided its herd mates by vaccination. The cost of at least one PI animal in a commercial beef breeding herd has been reported to range from $14-$24 per cow per year in reduced reproductive efficiency alone.
Research at West Texas A&M University found feedyard PI prevalence to be about 0.17% (1.7 PI's per 1,000 head). This research also indicates the probability of initial treatment for respiratory disease is 43% greater in cattle exposed to BVD-PI cattle in the same pen or an adjoining pen. Therefore, the cost of BVD virus infection is too great to leave to chance. It is recommended that all cattle entering your herd -- including your new bulls -- be screened for the BVD virus before they enter your operation.