BVD-PI (Bovine Viral Diarrhea- Persistently Infected) project is a function of the Montana State University Beef Quality Assurance program. It is a collaborative effort with the Montana Stockgrowers Association and Animal Profiling International, Portland, Ore. The project emphasizes how important ranch biosecurity is in preventing BVD and in the elimination of PI calves. It also emphasizes a management-over-medicine approach to herd health management.
Creation of PI calves
PI calves can develop in the uterus of the dam if the heifer or cow is exposed to the BVD virus during the first part of gestation â€” about 40-125 days after conception. In fact, this is the only way a PI animal is created.
Other important points: A calf is born PI will always be a PI animal. If an animal is not PI at birth, it can never become PI. Persistently infected females will always produce a PI calf.
Although a high percentage of PI calves die at or near birth, or at least by weaning, many PI calves survive can be healthy appearing and enter the breeding herd or be offered for sale. PI animals usually have a very high and persistent amount of virus circulating in their blood and other fluids. They are very efficient transmitters of BVD virus. The target of the ranch-based screening projects has been to keep PI cattle out of breeding herds.
The main negative health effects of BVD virus are that it can inhibit conception and cause abortion in susceptible females. BVD also suppresses the immune system. In some cases BVDâ€™s effect on the immune system is more critical than the acute effects of the virus itself. This makes controlling BVD at the ranch all the more critical and cost effective.
Of course, aborted fetuses, dead calves, deformed calves, heifers that will not breed or stay bred, and other suspected cattle should be tested for PI status routinely unless cause of death is known. Tissue from freshly dead cattle can also be submitted for analysis.
How it works...
The screening is based on a small ear-notch sample taken from an animal and analyzed at the lab for the presence of the BVD virus. The sample(s) is then sent off to the lab in Portland, Ore to determine if the animal is infected with BVD. This particular lab can assure next business day screening results.
It is advised to separate the infected animal from the herd and wait three weeks and retest the animal. This is done to confirm that the animal is PI and not transiently infected with the BVD virus at initial screening, which happens in rare cases.
Some feeders are asking ranchers to screen their herds before or at weaning. There was a ranch in the project that was encouraged by his feeder to screen his calves before shipping. In that case, the order buyer shared the cost of screening with the rancher. There also have been Montana PI project calves showing up on video sale listings and market websites as being PI screened. At least one Montana auction market operator is saying that PI screened calves are already easier to sell this fall. There also have been calls to the state coordinators from out of state cattle feeders who are asking for a list of ranchers who are entered in the screening project.
It is highly recommended that all ranchers, seed stock and commercial, who market breeding cattle screen those animals for PI status prior to sale if they were not previously screened. This will provide adequate assurances to both buyer and seller that breeding animals, bulls and replacement cows and heifers, are PI-free. If the animalâ€˜s health management history is unknown, buyers have every right to ask that they are screened for PI status prior to delivery.
Perpetual PI screening from a cow-calf management standpoint is not being recommended. It is suggested that once a rancher screens a herd according to the project protocol (whole herd screening), he or she can be reasonably sure of a PI-free cattle herd given the following management regime:
1) A proper vaccination protocol based on use of modified live vaccines.
2) A sound, common-sense biosecurity program.
3) Screening of all new additions to the cow herd.
In 2007 technical assistance, cost share funding and easy to use sampling kits for all participants will be offered. The goal is to enroll 100,000 head of cattle in this yearâ€˜s project.
For more information and/or project participation forms contact the Montana BQA office
at 406-896-9068 or go to www.mtbqa.org. There is also a link to this page on the Roosevelt County Extension Website and
feel free to contact your local MSU Extension Office to discuss more details on the
Key Points for Reducing or Eliminating BVD from Your Herd
- Mature cows do not need to be screened unless they have a positive PI calf.
- Individual ID is critical to match all samples with the animals tested.
- A plan should be developed to eliminate PI animals from the herd.
- There is no need to retest a negative PI animal.
- PI surveillance should include the necropsy examination of aborted fetuses, stillborns and preweaning deaths.
- PIs that live to be breeding females can horizontally transfer of the virus to other animals in the herd, and they will always produce a PI calf.
- Open heifers should be tested before purchase or before commingling with herd.
- Bulls should be purchased as BVD PI free.
- All calves purchased for grafting should have an ear notch sample taken.
- Recipient females in an embryo transfer program should be screened.
Test animals before bull turn out to avoid exposure of a PI during breeding.
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