ELISA testing for BVD
June 1, 2009
There are several tests a producer can utilize to see if cattle are harboring BVD virus or is persistently infected (PI). Acute BVD is not as big a concern as persistent infection – in which the animal can never get rid of the virus. PI 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.
Many stockmen are trying to determine the BVD status of their herds, testing their cattle and eliminating any PI animals. Several tests have been used to check for BVD, but one of the more reliable is the 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, ID, 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 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 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 – purchased from the lab or your vet or some other source. These tubes can be used for blood samples, or a skin sample such as an ear notch for just the BVD test.
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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 care except packaging to make sure vials are not broken during shipment.
“We recommend using a box, and packing the tubes with newspaper so they don’t rattle against one another and break,” says Howard. “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.”
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 one 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.”
“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. The tubes just need to be properly labeled with the individual animal ID.
Some people send ear-notches in individual plastic Ziploc bags, but it’s easier for the folks at the lab if the samples are in tubes.
“Then 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.
“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,” he says. “It’s only a four to five hour process from start to finish.”
They started doing these tests in December 2007.
“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.
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,” says Odom. “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.
“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 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 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.
“An animal that is PI negative today will always be negative,” says Odom. “And a PI positive will remain positive all its life and will be a daily risk to all the cattle it comes into contact with. Many producers are finding that the extra value they get for their tested calves is enough to continue testing their calf crop every year.
“When cattle are sold on video sales and special sales, the extra value that PI tested (guaranteed PI negative for BVD) calves bring will more than pay for the cost of the BVD test,” he says.