There are several tests a producer
can utilize to see if cattle are harboring BVD virus. Acute
infection, in which the animal becomes exposed, triggers an
immune response. The body fights off the infection and recovers.
This form of BVD is not as big a concern as persistent
infection—in which the animal can never get rid of the virus. PI
(persistently infected) calves are the result of fetal infection
with a certain biotype of BVD virus at an early stage of
pregnancy before the fetus’ immune system is fully developed.
The calf’s body can never rid itself of the virus because it
cannot recognize it as foreign and therefore does not mount an
attack against it.
infections can raise havoc in a herd, resulting in abortions,
sick calves, poor performance such as a drop in milk production,
less weight gain, reproductive inefficiency, and lowered
resistance to other diseases. But persistent infection is the
silent, sneaky thief. A PI animal continues to shed the virus
throughout its life and is a constant source of infection for
the rest of the herd.
Many stockmen are now trying to
determine the BVD status of their herds, testing their cattle
and eliminating any PI animals. There are a number of tests that
have been used to check for BVD, but most reliable is the newer
ELISA (Enzyme-Linked Immunosorbent Assay ) test. A number of
laboratories around the country (including any state diagnostic
lab) can run this test to check blood and tissue samples.
Jeremy Howard, of Biotracking (a
company that does the Bio-PRYN blood test for pregnancy
checking) says their labs can now do the ELISA test for BVD at
the same time the pregnancy test is run, if producers desire it.
The main lab is in Moscow, Idaho, with affiliate laboratories
around the U.S. and Canada. “We use the ACE (Antigen Capture
ELISA) kit provided by IDEXX, to do the BVD test,” says Howard.
Stockmen can elect to send in blood samples or ear notches (skin
samples) for this test.
According to Neal Odom, technical
sales representative from IDEXX, “Ours is the only ELISA kit for
BVD testing in the United States.” It is also the only USDA
licensed BVD virus test available. This test costs $3.65 to
check for BVD. If the stockman is sending a blood sample to one
of the Biotracking labs for a preg test ($2.25) the two tests
can be run on the same sample for a total of $5.90. There is a
small cost (14 cents each) for the tubes to contain the
samples—and tubes can be purchased from the lab or your vet or
some other source. These tubes can be used whether you are
sending blood samples, or a skin sample such as an ear notch for
just the BVD test.
Blood samples can be collected
any time cattle are in the chute (drawing 2 or 3 cc from a vein
under the tail, into the vial) and sent to the lab, without need
for refrigeration or any special care except packaging to make
sure the vials are not broken during shipment. “We recommend
using a box, and packing the tubes with newspaper or something
like that so they don’t rattle against one another and break. If
you are sending ear notches and a tube breaks, it’s not a
problem because we can recover it, whereas with a blood sample
we wouldn’t be able to,” says Howard.
Ear notch samples for the skin
test (if a stockman is just doing the BVD test and not the blood
test for pregnancy) are very simple to obtain. “We just need a
small piece about 1 centimeter square, taken from the ear,” says
Howard. “There are instructions on our website that show where
to do it on the ear. You can use an ear-notching tool, which you
can buy from us or any livestock supply store,” he says.
“A medium size pig ear notcher
works perfectly,” explains Odom. The notch can be taken from the
lower edge of the ear or at the center of the edge at the
outermost tip, whatever is easiest.
“When sending the ear notch
sample to us, we ask producers to put it into a red-topped
tube,” says Howard. “It can be shipped to us that way, without
having to put it in saline. Some of the other locations around
the U.S. require that you add saline, but we don’t. We do all of
that in-house here at our lab, in our controlled environment.
The producer doesn’t have to worry about that,” he says. The
tubes just need to be properly labeled with the individual
animal ID. The lab sends the report results back to the producer
exactly how the tubes were labeled (with cow name, number, or
whatever was written on the label).
Some people have sent ear-notches
in individual plastic Ziploc bags, but it’s easier for the folks
at the lab if the samples are in tubes. “We have to take them
out of the bags and put them into tubes. If they arrive in a
tube we just add a buffer solution and incubate that for a
period of time and plate it out and get it ready to go,” says
“When we get the ear notches, we
refrigerate them and run the tests once or twice a week when we
have a large number to do, so we can maximize the amount of
wells we use on the ELISA plate. If we start the test on Monday,
we get the results out to the producer (by phone, e-mail, fax,
mail or however the producer wishes to receive them) later that
day. It’s only a 4 to 5 hour process from start to finish. As
our number of samples increases, we will do the tests more
often,” says Howard. They just started doing the BVD tests in
December 2007 and already the numbers of samples being sent is
increasing; it won’t be long until they are running these tests
“Our lab is expanding its
facility, due to the increase in volume—both the BVD and the
pregnancy testing, and we’ve also added other testing to our
repertoire, such as goats and sheep,” says Howard. At this
point, however (not doing it daily) the turn around on results
from the ear notch test for BVD is not quite as fast as for the
blood test preg check, but the lab is willing to work with
producers; if they need the results immediately, the lab will
According to Odom, the ELISA test
is really the first pro-active diagnostic test the cattle
industry has had. “Much of the other testing that’s done is
reactive testing. The producer discovers he has a disease
problem and sends in samples to try to find out what it is. This
is a bit similar to trying to get the license plate number of
the car that just ran over you,” says Odom.
“By contrast, pro-active testing
is more like calling ahead to see what the road conditions or
traffic is like before you get there,” he explains. This BVD
test can be run on animals that are not sick, such as new
animals brought onto your place; they can be checked for PI BVD
status before they are ever added to your herd.
“It’s important to realize how
many cattle can be adversely affected by so few,” says Odom. One
PI animal in your herd can expose them all. BVD testing can be
an excellent part of a bio-security plan.
“The thing that made the biggest
impression on me when I looked at this 4 years ago was the
impact a few head can have. At first the producer might be
skeptical about spending that much per animal just to find 4
head per 1000 cattle tested. Typically in 1000 head (such as 10
loads of cattle being delivered to a feedlot) you’ll have one
load that has 2 PIs and 2 load that have one PI each,” he
explains. But those PI animals can expose the rest of the cattle
in their pen.
“Suddenly you’ve gone from 4
tenths of a percent to a 30 percent problem. Then you’ll be
putting those exposed cattle next to a pen of other cattle. Now
you are up to at least 60 percent exposed in your feedyard,”
“One of the things that really
made an impression on me, and one of the biggest take-home
messages for most producers is the risk to a herd from the PI
animal as opposed to the risk from a sick animal with just a
transient BVD infection. The one with the transient infection
will be sick for 10 days or 2 weeks and then he’ll be over it.
While he has the active infection he’ll shed about 10,000 viral
units per day. By contrast, the shedding rate from a PI animal
is about 1000 times that much, and he continues to do that every
day of his life,” explains Odom. You quickly realize that the PI
animal is by far your worst risk to the rest of the herd. Sooner
or later that animal will expose a pregnant cow during the
critical stage of gestation and this will result in another PI
The real cost of PIs and BVD in
general, however, is in decreased production in your herd—the
cows that abort or don’t settle, or have a live calf that dies
shortly after birth, or calf that dies later as a weanling or
“The main thing is to work with
your veterinarian on a good program to eradicate BVD if you have
it in your herd,” says Howard. “The veterinarians we work with
recommend that if a producer has not done any testing before,
they test the whole herd the first year, and eliminate any PI
animals. After that, they only need to test the calves born each
year, and any open cows, bulls, and any new animals they bring
onto the place.” If the calves are negative, this means their
dams are negative, and they don’t have to be retested. Testing
the calves is important, especially if any calves were conceived
somewhere else, such as on the range.
And if you buy some bred cows or
heifers, even if they themselves test negative, their calves
should be tested after they’re born. The dam may have been
infected during pregnancy, and even though she might be over the
transient infection by the time you buy her, the fetus might
have been affected—resulting in a PI calf.
Odom says that a good game plan
for a rancher is to first test all the calves. If a calf tests
negative, then the dam is also negative, and you don’t need to
test her. “Then test the open cows, the bulls, and all new
cattle introduced to the ranch. If everything comes back
negative, congratulations! You now have a low risk herd,” he
“It is important to know that an
animal that is PI negative today will always be negative. The
same is true for a PI positive; it will remain positive every
day of its life and will be a daily risk to all the cattle it
comes into contact with. Also, many producers are finding that
the extra value they get for their tested calves is enough to
continue testing their calf crop every year,” says Odom.
“The thing that’s very
encouraging, as cattle are sold on video sales and special
sales, is the extra value that PI tested (guaranteed PI negative
for BVD) are bringing. This more than pays for the cost of the
BVD test,” he says.
“Dr. Robert Fulton at Oklahoma
State University has been doing BVD control projects with the
Noble Foundation for the past 2 years. They enrolled all the
calves in a preconditioning program and sale through Oklahoma
Stockyards. Clem Ward, an economist at OSU gathered the sale
data. This last year, according to OSU, the PI tested calves
brought $4.65 a hundred over even the preconditioned calves. And
in calves sold through Superior (video market) there’s usually a
$2 to $3 premium on calves that are offered as PI tested,” says
Whether calves are being sold as
feeders, or replacement heifers, it’s worth the extra money to
the people buying them, to know they are not bringing BVD into
their feedlot or ranch. “It’s great to do the Vac 45
preconditioning; feed yards really need that done and it’s a
good program for producers if you are paid to do it. But if you
can also get the feed yard or buyer to pay a little more for BVD-PI
tested cattle, everybody wins. The feedyard gets cattle without
PIs and the rancher gets the benefit of knowing his BVD status
at the ranch,” says Odom.
Impacts Of PI Calves
“A research trial in Australia is looking at the impact of PI
calves on not only their pen mates but also on calves in
adjacent pens in a feedlot,” says Odom. On occasion there can
actually be more risk and adverse impact from a PI in the
neighboring pen than in the home pen.
A PI calf has a high shedding
rate and is constantly transmitting the virus to the animals
he’s in contact with. “If a PI calf and his penmates were all
raised on the same ranch or out on the range together, the
penmates may already have some immunity to that strain of virus
the PI calf is shedding, because they were exposed,” explains
Odom. But when this group of calves is sent to a feedlot, the
calves next to them may not have been exposed to BVD before, or
to this particular strain. They may be more apt to become sick
than the penmates of the PI calf.
“Another thing, that I’ve noticed
here in the U.S., is that penmates who were exposed to that PI
calf may not get sick for awhile because they have developed
some immunity, but if they get enough stress (weather, handling,
etc.) the stress may overcome that resistance and they get
sick,” says Odom. “The big advantage in a feedyard or a dairy to
finding the PI calves and getting rid of them is not necessarily
to eliminate the transient clinical, acute infections (in which
the animal is visibly ill), but to eliminate the chance for
sub-acute infections.” There’s a lot of profit robbing in the
lowered production of those animals. The illness may not be
severe enough that you notice it, but the animal doesn’t feel
quite normal and may not eat as well—therefore gaining less
weight or producing less milk.
Accuracy Of The Elisa Test
There are several options available for BVD testing, and these
vary in cost, turnaround time (when results are known) and
accuracy. Some of the older tests rely on virus isolation and
immunohistochemistry and these tests are relatively expensive
because they take a lot of time and labor.
PCR (Polymerase Chain Reaction)
tests are fairly recent. A single sample test is relatively
expensive because this type of test is also time and labor
intensive. Originally it was thought that the PCR test was so
sensitive it could find a positive in a large group (pool) of
samples, to help reduce the cost—the idea being that individual
retesting would only need to be done on a batch in which a
positive is found. But recent studies have shown the PCR test
for BVD to be only 85 percent accurate or less.
The IDEXX Antigen Capture ELISA
test (the newest test for BVD) has proven to be more accurate
and also requires less time and labor, making it the most
affordable single sample test. It can be done with blood or skin
samples, and most labs can provide test results the same day the
samples are received.
“There are several studies that
have looked at the Antigen Capture ELISA test versus the various
pooled PCR tests,” says Odom. “Every one of these studies have
basically stated our Antigen Capture ELISA is the most reliable.
Pooling will reduce cost, but in the pooled samples some of the
positives get missed. When you are possibly trying to find only
4 positive animals per 1000 to begin with, missing one or two of
those positives defeats the whole purpose of testing,” he says.
Several large ranches across the
country started doing some testing a few years ago and were some
of the early adopters of BVD testing. One more than one
occasion, a calf that tested negative was later found to be PI.
“If you are going to spend the money for testing, you need to
spend it wisely,” says Odom. Even though the Antigen Capture
ELISA test may be more expensive than doing pooled samples, it
is also more accurate. In the long run, it’s money well spent.
“Several years ago, when the PCR
test was developed, everyone was so excited that it could be so
sensitive it could pick up anything in a large group of samples.
But now we’re finding that there are other things that interfere
with those pools and it’s not as accurate as we once thought,”