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.
No matter what they look like physically, the real damage from PI calves is in further transmission of the BVD virus.
“A PI calf sheds hundreds of thousands of virus particles from all of its secretions, whether it be tears, saliva or even urine,” says Dr. Travis Van Anne, Professional Services Veterinarian with Boehringer Ingelheim Vetmedica, Inc. “That calf is shedding so many virus particles that it can overwhelm the immune system of animals he may come in contact with.”
Calves infected with BVD, whether PI or not, have a compromised immune system that puts them at risk for a host of other health issues, including scours and summer pneumonia.
“Cattle, and more specifically calves, exposed to the BVD virus are then more susceptible to every other disease agent they come in contact with,” Dr. Van Anne says. “Each challenge is going to be more severe and have a greater chance of decreasing the efficiency of that animal.”
Cows that come in contact with PI calves are also at risk.
“If you have a BVD virus that is highly pathogenic in your herd, you could experience a 40 percent open and late-calving rate,” says Dr. Van Anne. “You’re going to have fewer calves to sell, and the ones you have may be lighter due to significant health issues, or delayed calving. There is published data showing that those calves exposed to BVD are going to go to the feed yard at a lighter weight and may not perform well all the way to finish.”
On a herd level, the first two years of exposure to BVD is the time when the disease and financial impact are greatest. Dr. Van Anne calculates that — based on feed costs and the cost of replacement heifers/mature cows — each remaining bred cow will have to make up nearly $700 in lost production value.