Bovine viral diarrhea (BVD) affects cattle of all ages, in every herd size, worldwide and in every U.S. state. This aggressive enemy has infiltrated herds for 60 years. Testing can aid in defeating BVD, but eradicating the costly disease calls for dairymen to do their part in the fight as well. “It is possible to eradicate BVD from all dairy herds,” says Dr. Scott Smith, of The Dairy Authority (TDA) in Greeley, Colorado. “All it takes is compliance and cooperation.” Smith, who has practiced dairy medicine exclusively since 1999, is passionate about BVD control programs in cattle and oversees the IDEXX HerdChek BVDV Antigen ELISA Ear-Notch and Serum testing at TDA Lab.
Though BVD has reproductive and respiratory implications, the biggest problem is persistent infection that often goes unnoticed. BVD, first recognized in the 1940s, earned its name from profuse, bloody stool symptoms.
“It’s like HIV is to humans,” explains Smith. “It suppresses the cow’s immune system, making her highly susceptible to other infectious disease.”
It’s not just diarrhea or reproductive problems or even decreased milk production. A long list of illnesses includes infections, repeat-breeding problems, abortions, congenital defects, mucosal disease, and lowered resistance toward pneumonia, scours and other viral and bacterial disease.
“Anytime you have pregnant females, you run the risk of spreading BVD by creating the next generation of PI animals,” says Smith.
The virus crosses the placenta in infected pregnant cows, causing reproductive losses due to abortions, stillborn calves or calves that die early in life. When cows become infected early in gestation, some calves survive, becoming immunotolerant to the virus. Most calves with a persistent infection die before age two, but some live into adulthood, appearing healthy, only to shed a thousand times more virus than animals with transient infection.
“PI is how BVD makes its living – flying under the radar and going undetected, shedding BVD viruses every day,” says Smith. “The only way to find the PI animals is to test. You can’t control BVD by vaccination alone. You have to identify and eliminate the PI animals.”
PI animals are the main source of BVD transmission. A persistently infected cow produces a BVD-PI calf 100 percent of the time. If a PI- negative cow is exposed to BVD virus in her first trimester, 30 to 150 days gestation, there is a chance the fetus may be PI. On the bright side, it only takes one test to determine if calf and dam are persistent carriers. Since PI infection occurs only in utero, once it is determined that a calf is PI-negative, it will never become PI-positive.
TDA tests a number of dairies and in particular screens young animals, using the ELISA notch test on baby calves to address risks immediately. If a one-day-old heifer calf is negative, she is safe to go into the herd.
One of Smith’s clients models the discipline it takes to eradicate BVD-PI by enlisting tests and biosecurity measures.
This specific dairy raises 2,000 milking cows and replacement females. Heifers were originally sent off-site to breed, then returned to the herd. Initially the herd was screened in groups using a bulk milk Polymerase chain reaction (PCR) that looks for BVD.
“We found one positive pen, so proceeded with individual ear notches on all cows in that pen,” says Smith. “Of those we found one positive cow and she went to slaughter.”
At the same time females in milk production were screened, every calf born was tested. If the calf was negative, by default her dam was negative. “It’s another advantage of the IDEXX ELISA test,” says Smith. “You can test a calf and if found negative, determine the status of its mother, too. So in reality, you test two animals for the price of one.”
Bred heifers serviced off the farm were each tested upon their return and quarantined for three weeks.
“Often the quarantine period is overlooked when co-mingling cattle in any circumstance,” says Smith. “If a load of cattle comes in, they may not make springers sick, but they could be shedding enough BVD virus that would transmit to the developing fetus and render a PI calf. Three weeks’ isolation gives a chance for a transient BVD viral infection to run its course without infecting the herd they are being introduced to.”
This particular client of Smith’s now has a closed herd and is completely BVD-PI free. A follow-up PCR six months after the first check resulted in negative findings. It’s been more than nine months since they found the last PI calf. The herd was closed in January of 2009.
For only $4 to $5 per head, dairymen can have peace of mind and a far healthier herd.
“It’s simple,” says Smith. “It’s a one-day-turnaround test with extremely accurate results and it is USDA approved.”
Smith emphasizes testing is only one component of a complete BVD control program. “Proper vaccination, biosecurity and bio-containment are important issues when designing a comprehensive plan to deal with BVD,” says Smith.
“I’ve seen the results and it is doable,” he says. “There’s not a lot of maybes. We know if we take certain steps we can eliminate the BVD virus from these cattle populations and it’s one less thing we have to worry about. It is a fight we can win.” PD
Brenda Black is a freelance writer, author and speaker from Deepwater, Missouri.
To obtain a list of laboratories that process the BVDV Antigen ELISA Ear-Notch and Serum test mentioned in this article, contact Ron Kramer at email@example.com or (207) 347-1664.