Many cow-calf producers may ask why it’s necessary to test their herd for persistent infection (PI) of bovine viral diarrhea (BVD). After all, they reason, if a BVD PI calf is going to die anyway, won’t things take care of themselves?
Unfortunately, says Dan Givens with the Auburn University College of Veterinary Medicine, it just doesn’t work that way.
“The problem is that the PI calf has a negative impact on all the calves surrounding it,” he says. “Even up to weaning, there are indications that a PI calf in the group is going to negatively impact the growth of your other calves.”
Givens says BVD testing isn’t something that needs to be done on every calf in every situation. But there are some clinical signs that indicate BVD may be a problem in your herd.
“If you have lower-than-expected pregnancy rates; if you’re dealing with abortions; if you’ve seen some birth defects, low birthweight calves and poor calf health; if you’re seeing calf loss between birth and weaning; that’s a real indication that perhaps you have BVD in your herd,” he says. It’s also a strong signal that some diagnostics are in order.
Because a BVD PI calf can only happen during pregnancy, Givens says the goal is to prevent fetal infection. That starts with testing before breeding season begins – and testing calves, bulls and replacement heifers.
“If we get a negative test on a calf that’s naturally born from a cow, the cow is negative,” he says. “If it’s a positive heifer that doesn’t have a calf, she needs to be sold for slaughter. If you get a positive on a calf, understand that you need to get that calf and its dam away from the rest of the herd, because that calf is going to be spreading virus.”
Then test the cow. “If it’s a positive cow, you need to sell the cow and the calf for slaughter.” However, chances are very good that the cow will be negative. “Ninety-three percent of PI calves have a negative dam,” he says. “She had an acute infection during gestation, but she cleared that. Now, she’s the most immune cow on your entire farm.”
Givens recommends that you test and quarantine any new cattle that come onto your place for 21 days, unless they are verified as having tested negative for BVD.
And then, he says, make sure your vaccination program is in order, particularly with your replacement heifers. He recommends a modified-live virus (MLV) vaccine, realizing that if you vaccinate after the bulls have been turned out, it’s important to use an MLV product that’s labeled for use in pregnant cows. And don’t forget to vaccinate your bulls as well.