Bovine viral diarrhea virus (BVD) infection is responsible for a variety of economically important syndromes in beef herds. The economic losses from BVD infection will vary between herds based on herd immunity and stage of gestation at the time of exposure, the virulence of the BVD strain and other factors.
The virus is known to cause immune suppression, respiratory disease, infertility and fetal infection. Fetal infection (infection of the fetus during pregnancy) can lead to early embryonic death, abortion, birth defects, stunting, or the birth of persistently infected (PI) calves. Persistently infected cattle can result when susceptible pregnant cows are exposed to BVD virus during the first half of gestation and the virus passes from the dam to the fetus. Many times infected fetuses are aborted, but if a PI fetus survives to term, it will always have a tremendous amount of the virus in its body and cannot mount an immune response to clear the virus. A PI animal will secrete BVD virus throughout its life; in contrast to animals that become infected after birth that secrete the virus and are contagious for a few days to two weeks. These PI calves constitute the main reservoir and source of BVD virus for spread within the herd and to other herds of cattle.
Cattle persistently infected with BVD virus can be identified by a number of laboratory tests. Based on the NAHMS 2007-08 Beef Cow-calf study, while only 8.8% of U.S. cow-calf ranches had one or more PI animals identified; this means that one in every 11 to 12 herds have PI calves and most are not aware of their presence.
Vaccination programs can provide fairly good protection against BVD-induced disease when the exposure is from non-PI animals that are transiently infected with BVD. Vaccination programs offer some (but decreased) protection against BVD-induced disease when the exposure is from PI animals because of the tremendous amount of virus excreted by PI animals. Vaccination programs are an important component in BVD control, but will only offer a high level of protection if herd contact with PI animals is eliminated.
BVD consult
The cattle industry has made significant efforts in recent years to control BVD based on research that has provided a more complete understanding of the epidemiology of BVD, enhanced availability of diagnostic tests for detecting animals PI cattle, and a better idea of the economic impact BVD has on cattle herds. Our current knowledge of the epidemiology of BVD, the availability of efficacious vaccines, and the improvement in diagnostic tools have made the control of BVD feasible.
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DocTalk: BVD consult
Welcome to our DocTalk page on Bovine Veterinarian ! Each week Dr. Dan Thomson and his guests will discuss important issues related to livestock welfare and management, including current animal agriculture research, ways to keep the food supply safe and companion animal health issues. Dr. Thomson is an internationally recognized leader in beef cattle production and health management, and he serves as the director of K-STATE’s Beef Cattle Institute. His guests include nationally and internationally known veterinarians and animal scientists
New online tool helps producers and veterinarians make decisions regarding BVD management.
Stop BVD
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Bovine viral diarrhea (BVD) remains one of the costliest of cattle diseases, and a persistently infected (PI) animal can cause devastating losses at any production stage. To address the problem at a national level, NCBA has teamed with Animal Profiling International, launching a BVD surveillance program during the Cattle Industry Convention in Tampa. The program offers BVD testing at a reduced rate of $2.25 per head for NCBA members with no minimum. A PI calf can occur when a gestating cow is exposed to the BVD virus during the period between 40 to 125 days of gestation. The virus is transferred to the fetus, and if the calf is born alive, it can survive as a PI calf, constantly shedding the virus and infecting other cattle for as long as it lives. Exposure to a PI calf can cause annual losses from $15 to $25 per cow in a cow-calf herd and between $42 and $93 per head in a feedyard. In addition to the special price of $2.25 per head for testing, participants have access to telephone and e-mail support from a BVD expert at no extra cost, along with control and surveillance education. Testing results from participants in the program will be used to create a national surveillance system, but individual results are confidential and will not be shared with NCBA. John Patterson, PhD, who manages the program as NCBA’s executive director of producer education, says NCBA will track information on a state-by-state basis, but individual results will remain between producers and their veterinarian. Ultimately the group plans to use geographic data to identify hotspots to target for additional testing and education. Control begins at the cow-calf operation, where PI calves are created, but surveillance of disease incidence at feedyards can help identify where those calves originate. Patterson notes that testing can add value to calves marketed for feeding and heifers sold as replacements, as it reduces the buyer’s risk. According to recent data from Superior Livestock Auction, 2012 was the first year calves certified as BVD PI-free earned significant premiums in Superior’s sales. Those premiums averaged $2.42 per hundredweight. For more information on how to obtain test kits through the program and how to collect and submit samples, visit NCBA’s BVD surveillance website. For additional BVD resources and detailed information on BVD control and eradication, visit BVDinfo.org - See more at: http://www.bovinevetonline.com/news/Stop-BVD-191738571.html?source=related#sthash.YLRgjqxD.dpuf
Controlling BVD fetal infection
When designing a bovine viral diarrhea (BVD) control plan, vaccination for prevention of birth of persistently infected (PI) calves should be a primary target. As the principal source of fetal infection from BVD, PI calves compromise herd health and profitability, as they place the entire herd at risk.1
“PIs often serve as the source of BVD virus in the herd that can result in fetal infections the next year,” says Dale Grotelueschen, DVM, Pfizer Animal Health. “Targeting the prevention of PI calves allows producers to lessen herd risk of BVD fetal infection, including the development of more PI calves the following year.”
Understanding how BVD can be spread in a herd through PI calves is an important step in developing a solid control plan. Depending on the stage of gestation, the effects of fetal infection from BVD can range anywhere from infertility to compromised immune systems to persistent infection (Table 1).2
Table 1. Effects of BVD virus on unborn calves by approximate time of infection3
| |||
Gestation
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0–40 days
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40–120 days
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120–160 days
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160+ Days
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▪ Early embryonic death
▪ Resorption
▪ Abortion
▪ Return to estrus
|
▪ Persistently infected calves
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▪ Fetal anomalies/weak calves
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▪ Birth of calves with serum virus neutralizing (SVN) antibodies to BVDV (calves have functioning immune system)
▪ Increased risk of developing health problems
|
Although not all PI calves survive past 6 to 12 months of age, those that do often appear healthy and reach maturity. These PI calves typically shed the BVD virus heavily throughout their lifetime, making it difficult for dams, unborn calves and herdmates to escape infection.3,4
Once the role of PI calves is understood, producers should evaluate their BVD control plan for its long-term efficacy and ability to break the PI cycle.
“Producers who plan their health programs over a multiyear window can do a better job of preventing PIs by designing approaches that reduce risk for exposure and minimize chances for occurrence of fetal infection,” Grotelueschen explains.
Finally, to ensure a BVD control plan adequately protects a herd from PI animals, it’s important to choose a vaccine that provides the highest possible label claim for PI protection. Because fetal infection can occur at any time during gestation, a vaccine with year-long protection is also essential. Certain vaccines have been shown to provide duration of immunity for at least 365 days and prevention of BVD Types 1 and 2 PI calves. Vaccines like this provide producers with a convenient and flexible management system that requires less handling of cattle while increasing profit potential.
1 Baker JC. Bovine viral diarrhea virus: a review. J Am Vet Med Assoc 1987;190:1449-1458.
2 Bolin SR, McClurkin AW, Coria MF. Frequency of persistent bovine viral diarrhea virus infection in selected cattle herds. Am J Vet Res 1985;46(11):2385-2387.
3 Brock KV. Pathogenesis of BVDV infections. In: Bovine viral diarrhea virus. Available at: http://www.vetmed.auburn.edu/~brockkv/path.htm. Accessed June 29, 2009.
4 Tizard I. Immunity in the fetus and newborn. Veterinary immunology: an introduction. 4th ed. Philadelphia: WB Saunders Co, 1992:248-260.
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