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Tests For BVD
By Heather Smith Thomas
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.

Acute 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 Howard.

“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 every day.

“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 accommodate.

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,” says Odom.

“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 calf.

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 yearling.

“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 says.

“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 Odom.

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,” he says.

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