Worldwide, bovine virus diarrhea (BVD) is among the most devastating of cattle diseases. One reason for its widespread existence and persistence is 70-90% of all BVD virus infections occur without clinical signs, leaving most cases of BVD undetected in cow herds.
Clinical signs of the disease, including mucosal erosions and diarrhea, have obvious impacts on infected animals. But, beyond the acute effects of BVD, which can include death, most livestock managers are finding that animals infected with the BVD virus don't live up to their genetic potential.
Lower weight gains, increased disease susceptibility and diminished reproductive performance are indications the BVD virus may be present in a cow herd.
Time to make a move
After haunting ranchers and cattle feeders for decades, there's a movement afoot to stamp out BVD. Led by the Academy of Veterinary Consultants (AVC) and the American Association of Bovine Practitioners, concerted nationwide efforts are increasing. These efforts have a common denominator — a multi-faceted approach to the disease.
The key to controlling BVD on a micro or macro scale is vaccination, testing and diagnosis, as well as biosecurity, says Jim Kennedy, DVM, Rocky Ford, CO. He's director of the Colorado Veterinary Diagnostic Lab in Colorado State University's (CSU) College of Veterinary Medicine and Biomedical Sciences.
“The major source of BVD infection is persistently infected animals — or PIs,” Kennedy says. “PIs result from cows being exposed to the virus in pregnancy and the fetus becoming infected.”
Although such calves frequently show no signs of illness, they shed the virus in such great numbers that even well-vaccinated animals may become infected.
“Because most PIs in beef herds are nursing calves, and the virus is so immunosuppressive, many will die in early life of scours or pneumonia,” says Hana Van Campen, DVM, PhD and diagnostic virologist at CSU's Vet Diagnostic Lab. She adds that some PI calves will live for several months; in rare cases, for several years.
“In many herds, though, no adult carriers can be found,” Van Campen says. “This presents a diagnostic challenge in eradicating carrier animals from a herd. Nursing calves would have to be tested before the breeding season to break the transmission cycle.”
Type 1 vs. Type 2
In 1993, adult dairy cattle were dying suddenly in Eastern Canada and the Northeast U.S. Genetic typing found the BVD virus isolates were quite different than the recognized strains in existence.
“The new mutations were deemed Type 2 strains, and they have spread across the continent — including into and through beef cattle herds,” Van Campen says. “Many states and provinces are reporting Type 2 isolates as more common than Type 1.”
While vaccination is an integral part of any BVD control or eradication program, it alone won't control the disease. Over 140 BVD virus vaccines are licensed in the U.S., most of them produced from a Type 1 strain. Increasingly, vaccine companies are including a Type 2 strain in their products.
To provide broader protection, Van Campen says some producers are using a rotational vaccination schedule — alternating between different strains of Types 1 & 2. Vaccines are available as either modified-live virus (MLV) or killed. MLV generally provide better cross-protection against strains of BVD, than killed vaccines.
Most veterinarians recommend calves be vaccinated twice with an MLV before it leaves its herd of origin. Ideally, they say, BVD vaccinations should be completed at least 30 days prior to weaning. In addition, cattle new to the operation should be vaccinated before entering the herd, and isolated under a biosecurity plan developed with a local veterinarian.
Ultimately, Van Campen says the control of BVD virus-associated disease in beef cattle depends on the identification and removal of PI animals from the cow herd prior to the breeding season.
“This strategy has been outlined by the AVC, and is the basis of Colorado's voluntary BVD virus control and eradication program,” she adds.
Biosecurity in the mix
These days, biosecurity — and its relationship to controlling BVD — is one of Kennedy's passions. Through his leadership, Colorado is in its second year of a multi-level program designed to address the various components necessary to bring this disease under control.
For more information, contact the Colorado State University Veterinary Diagnostic Lab at 719/254-6382 or visit www.dlab.colostate.edu/BVDControlProgram/bvdcontrolprog_main.cfm.
“We're a long way from controlling BVD in Colorado,” Kennedy explains. “We're continually identifying PIs and herds experiencing abortions from BVD. We've got a lot of work to do.”
Once PIs are eliminated, a good biosecurity program will remove the worry of the financial and health impact BVD may have on a cow herd, Kennedy adds.
Three years ago, Lucy Rechel, the owner/manager Snyder Livestock, a cattle development center in Yerington, NV, took the BVD bull by the horns. What began as a screening program for PIs morphed into a full-blown biosecurity plan.
“We were tired of continually doctoring calves, and suspected much of our problem was due to PIs,” Rechel says. “We knew something had to be done to address this costly feedlot health situation.”
After a long hard look at the issue — and working with her local vet — Rechel called on some of the nation's leaders in BVD research and control. In the end, she developed a plan requiring BVD testing from all consigners to her 4,000-head feedyard (“Getting Serious About BVD,” March 2003 BEEF).
The idea was to keep PIs out of the feedlot by having ranchers test incoming bulls and heifers well ahead of shipping. The test of choice was the “ear notch” immunohistochemistry (IHC) test developed at the University of Nebraska.
Rechel has found enough success in her program that she now offers consigners an incentive to incorporate a comprehensive BVD biosecurity program — including a 30-day post-test quarantine.
“We'll be offering a feed discount to consigners who couple PI testing with a certified or a vet-approved BVD biosecurity and control program,” she says. “Testing for the disease is only part of keeping BVD out of a herd. It takes a total management program to eliminate and keep this disease out of a herd.”
Such a program, she says, could involve a multi-level effort like Colorado's, which includes a risk assessment, whole-herd BVD screening and elimination of PIs.
PCR helps the cause
Kennedy and Rechel say BVD testing has become easier with the advent of whole blood and ear-notch tests utilizing polymerase chain reactions (PCR), the latest diagnostic technology designed to detect DNA or RNA.
Two methods of implementing PCR to test for the BVD virus may be used — individual tests or pooled tests. The first, at $35/test, is prohibitive if you're testing a whole herd, Kennedy says.
However, by incorporating PCR technology and pooling samples, the PCR test can be quite cost effective and may be the best method for cattle owners who want to screen their herds for BVD-PI status, he adds.
For the pooled PCR test, white blood cells or tissue samples are collected. White blood cell samples are mixed in pools of 100 or less. When tissue samples are used, ear notches are soaked in a solution, and a small amount is collected and pooled.
The pooled tissue technique allows follow-up tests to be conducted without obtaining a second sample from the animal. The test's high sensitivity allows virus from a single infected animal to be detected, Kennedy says.
The cost of the pooled PCR can be as low as $50/pool, and is the most cost-effective test for PI-screening. Pooling allows owners to economically pursue a certified PI-free status.
Cattle feeders looking at PIs
Lately, there's been interest from commercial cattle feeders that may lead to further financial incentives to test and eliminate PIs from commercial cow herds. Since July 2005, the Rocky Ford lab has tested more than 40,000 ear notches using the pooled tissue technique.
“The majority of tests this fall were requested by feeders in southeast Colorado, western Kansas and northeast New Mexico,” Kennedy says. “Feeders realize that the cost of a PI animal in a feeding situation isn't acceptable, especially when there's technology to economically detect them.”
“We're seeing more interest from feeders who want to work with cow-calf producers to eliminate PIs before cattle leave the ranch,” he says. “Most have footed the bill on their own, but I expect more feeders next year will search out herds that have PI testing and control programs in place.”
Once feeders see a benefit to testing and eliminating PI cattle from their feedlots, PI-tested cattle could become the norm rather than the exception, he says.
Rechel is adamant that ranchers and cattle feeders who cooperate to eliminate PIs will save money in the long run. She's also very interested in seeing local vets and state animal health authorities develop BVD-free certification programs in their states and regions.
“We won't rid ourselves of this disease if we just have a feedlot here and a state there with control programs,” she says. “It's no longer as expensive to go through all the hoops needed to eliminate this disease.”
The time for control is now
Two meetings focusing on improved BVDV control in the U.S. will be held preceding the 2006 Cattle Industry Annual Convention and Trade Show in Denver. “BVD Control; The Future is Now” is set for Jan. 30-31, at the downtown Adam's Mark Hotel.
Research scientists, veterinarians, and laboratory diagnosticians with an interest in the control and eradication of BVD virus are encouraged to attend the Jan. 30 session. Topics to be addressed are: diagnosis and surveillance, control strategies and programs, vaccines, economic impact of BVD virus and development and funding of control programs.
Jan. 31 will focus on production-level control of the BVD virus, and detail what producers and practitioners need to know to prevent the disease and handle existing infections.
A detailed agenda and registration information is available at: www.nadc.ars.usda.gov/BVDV2006/.