In developing and executing biosecurity programs, veterinarians should consider more than just imported animals or neighbor’s cattle. The potential exists for the virus to enter a herd through embryo transplant, vehicles or equipment used on other ranches or at stock shows or through a non-licensed animal-health product with bovine components.
Mostly, though, the disease spreads via cattle during marketing, comingling and introduction to new herds. While the overall prevalence of persistently infection cattle remains relatively small, the possibility of importing one can be significant, especially in large operations. For example, Ridpath says, if the overall incidence is 1% and a 1,000-cow operation imports 100 bred heifers each year, the likelihood of bringing in a PI animal becomes quite high, unless the heifer supplier employs sound biosecurity and testing programs. When heifer raisers develop females for multiple operations, client must assume their heifers are exposed to every other animal at the heifer-development facility. Most professional heifer raisers are well aware of their BVD risk and engage in frequent testing, but the overall bred-heifer market often plays a role in introducing the virus to herds.
Importing a heifer that delivers a PI calf is one obvious risk, but the disease could move in the other direction. Ridpath says some ranches can have low-grade BVD infection circulating in their herd, with cows that have developed some tolerance to the disease. Reproductive losses probably are occurring, but at a low-enough level to avoid attention. When the operator imports replacement heifers with naïve immune systems, they can see disastrous abortion rates among those heifers.
Most large cow-calf operations and feedyards regularly test for BVD, but Ridpath says dairies could benefit by paying more attention to the disease. With year-around calving, dairies typically see more subtle losses in reproductive efficiency. Dairy managers who adopt sound prevention strategies find that “life is better without BVD,” Ridpath says. Dairies can use pooled samples from the milk tank to determine whether the BVD virus is present in their herds. If it is, they can move toward individual testing to identify and remove PI cattle.
In dairy and beef operations, managers should test all calves as early as possible. “There is no such thing as benign BVD,” Ridpath says, adding that it is best to get PI calves out of the herd as soon as possible.
Note: This article originally appeared as a part of "BVD Control: Multi-pronged approach" in the March 2017 issue of Bovine Veterinarian.