BVDV could be eradicated if we had the courage to go after it, researcher says
By Jean Caspers-Simmet
simmet@agrinews.com
Date Modified: 04/05/2012 1:57 PM
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CALMAR, Iowa — Julia Ridpath, research microbiologist at the USDA/ARS National Animal Disease Center in Ames, regards Bovine Viral Diarrhea Virus as low-hanging fruit as far as a controllable animal disease.
"We think BVDV is a disease that we could eradicate if we had the courage to go after it," Ridpath, who has been researching BVDV for nearly 25 years, told dairy farmers attending the recent annual meeting of the Northeast Iowa Community-Based Dairy Foundation.
Ridpath said research on animals coming into U.S. feedlots shows that two out of every 1,000 head are persistently infected with BVDV. At the calf level, it's likely higher.
Producers who buy 50 calves annually have a one in 10 chance of purchasing a persistently infected animal. Ridpath said that producers often say they have a closed herd, but they really don't. If an operation uses a heifer raiser, it's the same as buying calves into your operation and the risk increases the more operations a heifer raiser takes calves from.
"We don't really have closed herds," Ridpath said. "We have revolving doors."
Animals with persistent infection are just the tip of the iceberg, Ridpath said.
"A lot of BVDV associated disease does not result in a PI animal," Ridpath said. "All the planets have to be aligned. You have to get infection in the correct part of pregnancy. You have to maintain that pregnancy. The calf has to be healthy enough to live through birth and hit the ground to get a detectable PI. You have a lot of reproductive disease for every PI born on the place. A survey of a herd might show one PI among 1,000 animals, but that one PI indicates a whole lot of other things are going on to get that one PI."
The PI animal is not the big loss, it's the source of the loss.
"When you have that persistently infected animal on your place, it affects every neonate it comes in contact with," Ridpath said. "What does not kill you does not necessarily make you stronger."
Having a PI in a herd is the equivalent of vaccinating every day because that PI animal is constantly shedding virus and other animals have to respond immunologically, and they use energy to do that cutting meat and milk conversion.
There is increased virulence of secondary pathogens.
"Having BVDV around is like being nibbled to death by a duck," Ridpath said. "Things are just not doing as well as they should be."
Many silent reproductive problems exist. A smoking gun for BVDV is a well managed herd that doesn't have reproductive levels that they should have. Vaccination isn't a silver bullet and will not make PI animals go away if they're already in the herd.
"BVDV primarily affects the immune system, attacking the very system nature put in place to keep viruses out," Ridpath said.
Acute BVDV results from being exposed to PI animals. Severity will depend on the virulence of viral strain, the immune status of the animal, reproductive status and the presence of other pathogens.
"BVDV makes everything else look worse," Ridpath said. "It supresses the immune system, and it may directly interact with a second virus. It is the terrorist of viruses."
BVDV is spread by direct or indirect contact with mucus membranes — one animal coughing in the face of another, licking a post, sharing feed, salt blocks or water, or during breeding.
Controlling BVDV requires a three-pronged attack — surveillance to detect, biosecurity to prevent viral entry onto farms that don't have BVDV or biocontainment to prevent viral spread within a farm where BVDV has been detected, and vaccination to limit the negative impacts of BVDV on cattle health and production, Ridpath said.
For more information about Bovine Viral Diarrhea see www.bvdinfo.org. Producers with BVDV problems can contact Ridpath at (515) 737-7586 or julia.ridpath@ars.usda.gov.