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.
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.
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
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.