However, since colostral antibodies are effective in preventing infection in young animals, the disease is seldom seen before 3 months of age when management includes adequate feeding of colostrum from immune dams. Persistent infection PI carrier only develops in utero, and then only if the dam is exposed to BVDV, at less than days of pregnancy. An animal cannot become persistently infected after it is born. BVDV infection is diagnosed on the basis of the clinical signs plus confirmation through necropsy findings and laboratory tests of blood samples.
If blood is drawn during the acute phase of the disease the laboratory can often isolate the virus from the white blood cells buffy coat. If two serum samples are obtained, one in the acute phase and one a few weeks later, a rise in serum antibodies SN test between the two samples also confirms BVDV infection. When abortion is the only sign, diagnosis is often more difficult.
In these cases it is important for your veterinarian to submit the aborted fetus and placenta, in addition to serum samples from the dam, to the laboratory for testing. The persistently infected PI carrier animal is easy to detect. This animal sheds so much virus that a viral antigen in its serum readily confirms its condition.
Therefore, other test methods have been developed, including skin notch testing and whole blood viral DNA detection that can be applied to baby calves and also older animals. If BVDV gets into a non-vaccinated or improperly vaccinated herd, it will spread from animal to animal. Thus it is important to maintain a strong BVDV vaccination program that will minimize this type of transmission and allow containment of the virus before it infects a large portion of the herd.
Keep in mind that cattle exposed to the virus at less than days of pregnancy may give birth to persistently infected calves. These calves, if not removed from the herd, will serve as a continuous source of the virus that will perpetuate the disease in the herd.
Consequently, once BVD occurs in the herd, all calves born over the next 12 months should be tested for persistent infection. If any such carriers are detected, they must be removed from the herd immediately. It is best to test calves for persistent infection at birth or as soon as possible thereafter.
An effective BVDV prevention program is based on maximizing immunity and minimizing exposure of the herd to the virus. BVD vaccines are an important part of the prevention program. Vaccines are available in two forms - modified live and killed. Both forms have their advantages and disadvantages. An advantage of modified live BVD vaccines is that they stimulate the entire immune system both cell- mediated and humoral immunity.
Therefore, it is generally recommended that every animal receive a modified live BVD vaccine at least once in its lifetime, preferably when it is months of age. A disadvantage of modified live BVD vaccines is there may be label restrictions against using them on some or all pregnant animals, thus their use in mixed populations of bred and open animals must be carefully controlled. An advantage of killed BVD vaccines is that they can be used on all open and pregnant animals, thus the entire herd can be vaccinated at any time.
Disadvantages of the killed BVD vaccine include: a shorter duration of immunity, a reduced ability to stimulate cell-mediated immunity, and sometimes a slight drop in milk production for a day or two after vaccination. As indicated on the label, killed vaccines must be administered twice two or three weeks apart if the animal is being vaccinated for the first time.
Only one shot is required thereafter at 4 to 6 month intervals. Both types of vaccines, if administered properly and according to the label, will provide sufficient immunity to prevent the clinical onset of acute BVD. To maintain this level of immunity, the modified live vaccine needs to be given at least annually, and the killed vaccine needs to be given every months. Some clinical trials indicate superior protection of the fetus by certain MLV vaccines against some strains of virus.
Vaccines are a tool for prevention, not a cure. Bovine viral diarrhea virus BVDV is a significant pathogen associated with gastrointestinal, respiratory, and reproductive diseases of cattle worldwide. It causes continuous economic losses to the cattle industry primarily due to decreased reproductive performance.
The ability of virus to cross the placenta during early pregnancy can result in the birth of persistently infected PI calves. Animals with acute infection may be able to recover from the disease and are not BVD carriers. Whole herd screening tests all animals in the herd. Fortunately, by testing the calf we also know the status of the dam. If a calf is negative then his mother is negative as well, so we get the benefit of testing the pair for one test fee. However, if the calf is positive the dam needs to be tested because she may not be BVD positive.
If the dam is negative not a PI , the likely source of BVD fetal infection was dam exposure during gestation acute BVD infection to another infected animal in the herd. Having documentation of BVD test-negative animals aids in marketing cattle.
As mentioned earlier BVD negative feeder calves have sold for premiums in some marketing programs. After a herd has been test-negative for a few years, it is only necessary to test the market animals and all additions to keep adequate surveillance on the herd BVD status. This test is not approved for mixed samples pooling to reduce costs and may result in a false negative test animal tests negative when in fact is infected.
The individual ACE test is the most common test used because it offers rapid results with the fastest turnaround time. PCR can be used to run several samples pooled together in a single test. That is why it can be used with pooled samples. For PCR, up to 24 samples can be combined in a single test which can reduce testing costs significantly. IHC is a tissue staining technique to identify PI animals. The tissue is fixed in formalin, stained to target BVD virus infected cells and examined under a microscope.
It is highly recommended to retest cattle that test positive with the ACE or PCR tests weeks later to determine if the animal is a PI or temporarily infected. Cattle with a temporary BVD infection often clear within 4 weeks. However, if a pool tests positive, then all the pooled samples have to be run individually by ACE to identify the PI animal s , which requires additional time days and costs.
If time is critical, we suggest that you request the ACE test upfront. PCR testing is recommended when the number of samples to be tested is higher than Fees may change without notice. Check website for most current fees; www. There are a lot of laboratories from which to choose for BVD testing. It is important to select a lab that has a verifiable quality control process and uses the correct tests in the correct way. False negative tests are worse than false positive because it gives a false sense of security and increases the chances of infecting other cattle.
The Georgia Veterinary Diagnostic Laboratories in Athens and Tifton undergo regular quality reviews to verify their lab procedures are as accurate as possible. If you suspect your herd may be affected quick action to find the source of infection can help reduce the damage by this potentially devastating disease.
If your herd is not performing to your expectations and you have higher than expected calf loss or too many open cows, it may be worth investigating whether BVD is the cause. The UGA veterinary diagnostic laboratories provide diagnostic guidance and assistance to veterinarians and Georgia farmers that desire information about eradicating BVD or other potential disease agents from their herds. Further information about the tests, prices, and turn-around time can be found at www.
Reproductive losses caused by BVD or other diseases are preventable. Farmers are encouraged to work with their veterinarians to develop a good herd health program and achieve optimal reproductive efficiency in their herds.
Contact your local veterinarian, county extension coordinator or the UGA Veterinary Diagnostic Laboratories for more information if you think BVD testing might help you and your herd. Home News Bovine Viral Diarrhea. Bovine Viral Diarrhea.
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