When designing a bovine viral diarrhea (BVD) control plan, vaccination for prevention of birth of persistently infected (PI) calves should be a primary target. As the principal source of fetal infection from BVD, PI calves compromise herd health and profitability, as they place the entire herd at risk.

“PIs often serve as the source of BVD virus in the herd that can result in fetal infections the next year,” said Dale Grotelueschen, Pfizer Animal Health veterinarian. “Targeting the prevention of PI calves allows producers to lessen herd risk of BVD fetal infection, including the development of more PI calves the following year.”

Understanding how BVD can be spread in a herd through PI calves is an important step in developing a solid control plan. Depending on the stage of gestation, the effects of fetal infection from BVD can range anywhere from infertility to compromised immune systems to persistent infection, as indicated in the following table.   


Effects of BVD virus on unborn calves by approximate time of infection


0–40 days

40–120 days

120–160 days

160+ Days

Early embryonic death



Return to estrus

Persistently infected calves

Fetal anomalies/weak calves


Birth of calves with serum virus neutralizing (SVN) antibodies to BVDV (calves have functioning immune system)

Increased risk of developing health problems


Although not all PI calves survive past 6 to 12 months of age, those that do often appear healthy and reach maturity. These PI calves typically shed the BVD virus heavily throughout their lifetime, making it difficult for dams, unborn calves and herdmates to escape infection.

Once the role of PI calves is understood, producers should evaluate their BVD control plan for its long-term efficacy and ability to break the PI cycle.

“Producers who plan their health programs over a multiyear window can do a better job of preventing PIs by designing approaches that reduce risk for exposure and minimize chances for occurrence of fetal infection,” explains Grotelueschen.

Finally, to ensure a BVD-control plan adequately protects a herd from PI animals, it’s important to choose a vaccine that provides the highest possible label claim for PI protection. Because fetal infection can occur at any time during gestation, a vaccine with year-long protection is also essential. Certain vaccines have been shown to provide duration of immunity for at least 365 days and prevention of BVD Types 1 and 2 PI calves. Vaccines like this provide producers with a convenient and flexible management system that requires less handling of cattle while increasing profit potential.

To explore the available options, work with your veterinarian to evaluate your vaccine’s label claim and duration of immunity.

Source: Pfizer Animal Health