More About Sampling
According to the Montana Beef Quality Assurance website, and its state-wide BVD control program, here’s an example of how a partial herd screening protocol may be implemented:
• The screening process is typically based on analysis of “pooled” tissue samples (usually 28 or fewer tissue sample per pool).
• If a pool is “positive” for the virus, the individual tissue samples contributing to the pool are individually retested. Individual animals carrying the BVD virus can be identified by matching the tissue sample to the animal’s identification number.
• Once an animal is identified as a virus carrier, the animal (and its dam, if still nursing) should be segregated from the herd and held for re-sampling three to four weeks later. The second tissue sample should be submitted to the lab for a confirmation test in order to segregate transiently infected animals from PI animals.
Other elements to consider:
• Sampling is based on a small ear notch – about the size of a pie-shaped piece taken from a dime – placed in a dry tube kept cool or frozen.
• The same tissue sample used for initial PCR screening is the source sample for re-testing to identify individual “reactors” in the pool.
• Cows do not need to be sampled and tested unless they have a positive PI calf. In the case of a PI calf, the cow should be identified, sampled, and tested.
• Individual identification is critical to match all samples with the animal tested and match the calf with its dam.
• If an animal tests negative for BVD-PI status, there’s no need to ever retest that animal.
• PI surveillance should include the sampling and testing of as many aborted fetuses, stillborns, and pre-weaning deaths as possible. Screen all cows that lose a calf if a tissue sample was not obtained from the calf.
• PIs that live to be breeding females can horizontally transfer the virus to other animals in the herd – increasing the risk of more PI calves being born during the next calving season.
• Ear notches can be frozen for up to 30 days, facilitating sampling over an extended period of time.
• Purchased bred heifers or cows with an unknown BVD-PI status should be kept separate from the resident herd until their PI status can be confirmed. Calves from these animals should be screened prior to commingling.
• All non-biological pairs should be screened for PI status.
• PI animals should be removed from the herd and euthanized as soon as discovered.