A screening protocol developed with a consulting or practicing veterinarian will help the cattle producer with a herd at risk for bovine viral diarrhea (BVD) in finding all persistently infected (PI) animals.

BVD PI screening should be part of a program involving biosecurity, vaccination and overall herd health.

Key points:

• BVD PI testing should be based on the protocol of the lab and advice of a veterinarian.

• Test all calves in the herd before bull turnout to avoid exposure of a PI during breeding.

• Cows don't need sampling and testing unless they have a positive PI calf, assuming the calf can be matched to the dam.

• The PI animal needs to be eliminated from the herd. Remember, “Once a PI calf, always a PI calf.”

• If an animal tests negative for BVD PI status, there's no need to ever retest it.

• PI surveillance should include post-mortem exams of as many aborted fetuses and stillborns as possible.

• PIs that live to be breeding females horizontally transfer the virus to other herd animals — and will always produce PI calves.

Test new entries:

• Home-raised yearling heifers should be tested for BVD PI status prior to breeding. If the heifer was tested as a calf and found negative, there's no need to retest.

• Test open heifers before purchase or commingling with the new herd, and the start of breeding season.

• Keep all purchased cows with unknown BVD PI status separate from the new herd. Test their calves prior to commingling.

• Only use bulls that test BVD PI free.

• PI test all calves purchased for grafting.

• Test all open cows not sold before breeding.

• Cows that have not calved at the time of testing the other calves should be separated. Take samples from their calves before commingling.

• Test all cows losing a calf (if a sample wasn't obtained from the calf).

John Paterson, Montana State University-Bozeman; and Bruce Hoffman, DVM, Manhattan, MT.