Testing, vaccination keys to BVD PI management

by Mark Parker

Think of BVD PI as the Al-Qaeda of cattle health—an unseen terrorist cell waiting to wreak havoc and recruit more bad guys than you’d ever want to run into.

Persistently infected (PI) BVD cattle are a wreck that doesn’t wait to happen because every day a PI animal draws breath, it’s a threat to healthy cattle.

The consequences are troubling enough that a large crowd of beef producers showed up near Erie, Kan., last week to learn more about diagnosing and managing the problem.

Pfizer Animal Health Veterinarian Mitch Blanding of Lenexa, Kan., explained that a PI calf is created when a cow is infected with the bovine viral diarrhea virus 40-120 days into her gestation. That’s when the calf’s immune system is developing and the fetus fails to recognize the virus as an infection, incorporating it instead as a normal part of its makeup.

That guarantees the calf will manufacture and profusely shed BVD cells its entire life.

The PI calf may be aborted, it may be stillborn or it may be a poor-doing calf. Or, it may appear to be as normal as any other calf in the herd.

Blanding explained that more than 50 percent of PI calves don’t survive past 12 months of age. A few, however, make it to maturity and that’s when the other shoe drops because, in addition to spreading the virus in abundance, the PI cow will always, always, always have a PI calf.

“You can’t tell visually if a cow or calf or bull is a PI,” Blanding said. “Some PI cattle appear to be completely normal but you can count on one thing—however long they survive, they are going to spread BVD.”

PI cattle, he said, are the number one source of BVD infection. In the cow herd, PI calves can infect susceptible females and create even more PI calves. For backgrounders and feedlots, PI calves infect pen and pasture mates, causing serious health issues. Complicating BVD diagnosis is the fact that victims normally succumb to other non-BVD health problems. Reproductive losses are highly associated with the disease as well as a suppression of the immune system which can lead to a variety of health maladies, especially respiratory disease.

“For the cow-calf operation, it can show up in reduced pregnancy rates, in a lower percentage of calves weaned, in lower weaning weights,” Blanding said. “If you don’t keep records, it may seem very subtle but it can have a significant economic impact.”

BVD is spread by any bodily fluid secreted by an infected animal. Nose-to-nose contact is the most common vector since the virus cannot live very long outside of the animal’s body. Whitetail deer can also spread the disease and producers should consider their farm’s biosecurity—possible exposure to neighboring cattle and the introduction of untested animals into the herd.

Blanding discussed Pfizer’s Bovi-Shield Gold vaccine which provides 365-day protection against BVD Types 1 and 2, thereby preventing persistent infection during the critical 40-120-day fetal period.

Vaccination goes hand-in-hand with a testing program, Blanding noted and IDEXX Laboratories Technical Services Representative Ron Kramer of Leoti, Kan., outlined his company’s BVD antigen test. The only USDA-licensed test for identifying BVD in PI cattle, it begins with taking a tissue sample, typically a small notch from the animal’s ear.

The test costs about $3.50 per animal and the turn-around time can be expedited for rapid removal of PI cattle.

SEK Genetics at Galesburg, Kan., now offers BVD testing, utilizing the IDEXX system. Owner Don Coover emphasized that, while impact of BVD can be enormously dramatic, it can also be elusive.

“This is a disease that can be subtle,” he said. “If I felt the performance of my cow herd was less than it should be—too many open or late-calving cows—and I didn’t know why, BVD would be very high on my list to check.”

He suggested that producers concerned about the disease consider testing all calves born to a cow on the farm. Since PI calves come from PI cows, testing the calf crop, in effect, checks both dam and offspring.

Cows that don’t have live calves—without apparent reason—are also high on the suspect list.

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