Bovine viral diarrhea (BVD) virus may seem like a needle in a haystack, but that “needle” causes a host of concerns to cattle production worldwide.
Estimates of the prevalence of persistently infected (PI) animals in the U.S. beef cattle population range from 0.13% and 2.0%. And, about 4-10% of U.S. beef herds are expected to have at least one PI animal.
For the majority of producers, the bottom line in BVD control is in the economics. Control efforts simply have to pass the muster of measurable and positive cost/return ratios.
There's little argument that PI animals are “created” at the cow-calf level. Thus, solutions need to come from that sector.
“Losses due to this virus will continue until effective actions are taken within cattle operations to prevent further transmission,” says Dave Smith, University of Nebraska-Lincoln Extension veterinarian.
Understanding of the BVD virus epidemiology has advanced and, with recent developments in diagnostic methodology, it's now possible to control the disease.
Consulting veterinarian Bill Hessman, Haskell County Animal Hospital, Sublette, KS, says BVD is a disease that's been around cow-calf operations for a long time.
“But most cow-calf producers have become comfortable with BVD even though it costs the industry about $2 billion/year,” Hessman says. “I hear a lot of veterinarians say they don't have BVD in their area. But, I think we've under-diagnosed BVD.”
He agrees with estimates that up to 10% of U.S. cattle herds are sending PIs into the production chain. Hessman's adamant that first and foremost, PI calves shouldn't be welcomed at the feedyard level.
“We're advising our clients to go back to their backgrounding yards and test and remove PIs before they get to the feedyard,” he says.
The costs of BVD
Hessman, who also operates Central States Testing, LLC, has investigated the cost of BVD in High Plains feedlots for several years. He's tested 600,000-700,000 head of cattle from Florida to California. Work at Cattle Empire Feedyards, Santana, KS, shows BVD virus exposure from a PI calf in a pen costs $47/head for every animal going into the feedyard.
But he is seeing the evolution of practical and relatively inexpensive ways to address this disease. “There's no excuse for it to remain a herd health problem,” he says. “Cattle Empire Feedyards is now PI free, and we'll do everything we feasibly can to stay that way. The return we're seeing more than justifies a $4-$5/head investment into testing for PIs.”
Hessman says the recognition of the cost-effectiveness of testing and eliminating PIs will eventually — possibly sooner rather than later — lead to a BVD-PI free “price-discovery process” because of reduced treatment costs and improved performance within PI-free herds.
“We can enjoy a significant savings in overall costs if the feedyard is entirely PI-free,” Hessman says.
Costs beyond testing include the labor to collect samples, record maintenance, facilities to segregate cattle, and further management regimes to prevent BVD transmission.
Patsy Houghton, Heartland Cattle Company, McCook, NE, says ranchers should look at BVD PI control as an investment, not an expense. And she says attention needs to be aimed at the cow herd.
“If ranchers can keep BVD virus from reaching the fetus, they prevent PIs from ever being produced,” she explains. “As an industry, we can't afford PIs in our herds.”
She recommends some areas where ranchers should invest in BVD control:
- Purchase source-verified cattle,
- Purchase and administration of proper vaccines,
- Spend money for testing and diagnosis, and
- “Realize” all PI positives.
Included in the calculation of the cost of PIs should be the elimination of PI animals. Houghton recognizes PIs are a liability and shouldn't be sold into market channels where they can infect other animals.
In fact, many ranchers who've experienced BVD outbreaks report that in the long run it's more cost-effective to simply euthanize PI animals rather than pour money into treatment.
Bob Larson, DVM, PhD and director, Veterinary Medical Extension and Continuing Education, University of Missouri-Columbia, agrees the cost of PIs goes beyond the ranch.
“A reliable demonstration of PI-negative status may add market value to seedstock or commercial cattle,” he says. “We just can't afford to have PIs move into other production systems, such as heifer development operations or backgrounding, stocker or finishing situations.”
Larson, Hessman and Houghton agree that screening for PIs needs to be incorporated into an overall farm and ranch biosecurity and vaccination system.
The role of immunity
Vaccines' main role for many years has been to stimulate immunity against BVD virus.
More recently though, vaccines are being looked at to prevent transient (temporary) infection in susceptible pregnant females and reduce birth of PI calves when exposure does occur, says Dale Grotelueschen, Pfizer Animal Health senior veterinarian.
“Vaccines administered prior to breeding have reduced fetal infection resulting in fewer PI calves following experimental BVD virus challenge,” he says.
But vaccination alone hasn't proven an effective strategy for eliminating BVD virus from cattle herds, Smith says. Nor does vaccination entirely prevent birth of BVD PI calves, even though the risk may be reduced.
Additionally, even in the absence of vaccination, the number of PI animals and the amount of BVD virus infection in a herd seem to be self-limiting unless the herd has a lot of additions, Larson says.
Once the PI animal is in contact with the breeding herd for a sufficient period of time, the majority of the herd should become infected, and produce immunity that protects against further disease.