Cattle persistently infected with bovine viral diarrhea (BVD) can drain the production efficiency and profits out of a herd. By understanding how persistently infected cattle result and taking steps to prevent the problem, producers can safeguard their herds and their wallets against losses.Persistently infected (PI) calves are those calves born from cows exposed to the BVD virus at 30 to 150 days of gestation. An infected cow will transmit the virus to the fetus, and the calf is born persistently infected with BVD.

Some PI calves are easy to spot. They’re smaller than their herd mates and struggle with health problems. However, other PI calves may not show symptoms, and you may not be able to tell them apart from healthy calves.

Source