Staying On Top of BVDV
Continued control requires remaining vigilant.
Just a few short years ago Bovine Viral Diarrhea Virus (BVDV) was a buzzword in the beef industry – with the disease commanding headlines and garnering action from beef producers to test and control it in their cattle herds. Today, some of that focus seems to have faded, but veterinarians say that does not mean the battle against BVD control has been won.
They remind cattle producers that it is still important to stay on top of BVDV and biosecurity methods to keep cattle at the farm or ranch and in the feedlot protected.
David Smith, a professor and Extension dairy/beef veterinarian at the University of Nebraska-Lincoln’s School of Veterinary Medicine and Biomedical Sciences, explains that awareness of BVD was high a few years ago, which he attributes to the new testing capabilities – specifically ear notch tests – that allowed for easier detection of animals persistently infected with the BVD virus.
Smith says, “As testing increased, more BVDV-PI cattle were found and awareness grew. Some cattlemen recognized that BVD was in their herds, and they used testing to eliminate it; others used testing to keep the virus out of their herds with new additions, others for value-added marketing. Since then, many testing labs have started offering BVDV testing to service the increased demand for testing.”
As a result, Smith says the tools for effective BVD control are readily available (e.g. tests, vaccines, quarantine) and, he says, “Some cattlemen are making use of them to protect their investments.”
Risk still exists
However, on the other side of the coin, Smith says too many producers continue to take risks that allow BVDV to spread into their herds. He emphasizes that successful BVDV control requires not only an emphasis on vaccines and testing, but also diligence with biosecurity and the management practices to control transmission.
Dan Givens, Professor and Coordinator of Animal Health Research at Auburn University’s College of Veterinary Medicine, shares a similar perspective.
He notes that over the last few years, some progress has been made in preventing dramatic clinical illness due to BVDV. However, Givens says, “This progress has allowed the virus to fill an often undetected role in causing reproductive losses, suboptimal growth rates in calves, and immunosuppression during commingling of cattle.”
Givens emphasizes to producers that the critical steps in battling BVD continue to be:
1) Appropriate surveillance to detect BVDV if it is associated with disease conditions on the farm.
2) Biosecurity to prevent viral entry onto a farm which does not have circulating BVDV, or biocontainment to prevent viral spread within a farm where BVDV has been detected.
3) Appropriate immunization to limit the negative impacts of BVDV on cattle health and production.
Specifically, Givens says, “Ongoing research continues to improve our understanding of the negative impact of BVDV on the reproductive health of bulls. Clearly, bulls to be used for breeding purposes need to be protected from untimely and inappropriate exposure to BVDV.”
Additionally, he says, “To optimize immunological protection, heifers and cows should be adequately immunized before breeding with a modified-live vaccine which provides validated fetal protection. Furthermore, bulls should be vaccinated with a modified-live vaccine at six months of age and again at least 30 days before breeding.”
Likewise, Nebraska’s Smith says, “I think the next steps in controlling BVD transmission need to help more producers understand the risk they take from introducing BVD, create value within the industry for BVD control efforts, and show more producers what they need to do to protect their own herds.”
Smith points out that there are only three strategies for controlling the spread of contagious diseases like BVD: 1) improve immunity (e.g. vaccinate); 2) keep the agent out of the herd (e.g. test); and 3) prevent contacts that result in transmission (e.g. segregate, quarantine).
He says, “It is very important how these are used. It is rare that any one of these strategies is successful alone, but in combination they can be very powerful. Applying these three strategies together makes BVDV one of the most controllable contagious diseases of cattle.
“And, once producers understand and value BVDV control, they can learn how to modify those actions to control other important contagious diseases in their herds such as Johne’s disease, salmonellosis, mastitis, and trichomoniasis.”
Looking to the future, Givens notes that novel diagnostic tests continue to be developed to aid in detecting animals infected with BVDV. He says, “Tests for individual animals that can be performed rapidly on the farm will provide advantages within some segments of the cattle industry.”
While that technology will be beneficial, Smith says it will go hand-in-hand with continued biosecurity so that producers can be vigilant about BVDV and other pathogens that threaten the productivity of their herds.
BVDV Symposium Scheduled for November
“Preventing, Detecting, and Controlling the Spectrum of Diseases Caused by BVDV” is the focus of the 5th U.S. BVDV Symposium to be held Nov. 17-18, 2011, in San Diego, Calif.
The event will include scientific sessions on diagnosis, surveillance, and vaccination protocols of the disease, as well as updates on viral characteristics and the emerging epidemiology of BVDV in hosts other than cattle.
To see the full schedule and register online, see www.bvdvmtg2011.org.
Since inception in 2002, the U.S. BVDV Symposia have been a great opportunity for researchers, practitioners, and technical services veterinarians involved in all aspects of BVDV research to meet and share ideas.
Modified Live Vaccine Important for Successful Control
Burwell, Neb., veterinarian Brett Andrews believes much of the success in controlling BVDV over the past decade can be attributed to the use of modified live vaccines. Andrews notes today that he does see fewer persistently infected (PI) BVDV calves than he has in the past, and says often herds that do experience PI calves either were not vaccinating at all or were using a killed vaccine.
Andrews is one of four veterinarians with the Burwell Veterinary Hospital in central Nebraska. Seventy-five percent of the practice’s business is cow-calf and Andrews has been there since 1989.
He says, “BVDV and Red Nose are the two main reproductive problems we see in cow-calf herds. Our philosophy here hasn’t changed in 25 years – we recommend using modified live vaccines. I believe we may be seeing less PI-BVDV calves today because more producers are using modified live vaccines.”
His advice to producers is straight-forward: “Quit being afraid of modified live vaccines. You just have to know when and where to use them.”
Andrews says BVDV vaccinations are important for all calves at or before weaning and annually 30 days pre-breeding for bulls and cows. And, for replacement heifers going back into the herd, he recommends three modified live shots – at pre-weaning, after becoming a yearling in conjunction with a vibrio/lepto vaccination; and 30 days pre-breeding.
He notes that unusual death loss – particularly around weaning time – can be a clue that BVDV and PI calves are a problem in the herd. Other signs might include lower-than-expected pregnancy rates, an increased number of abortions, and low birthweights or poor calf health.
Those are indications that some testing should be considered to determine if PI animals are in the herd.
What Animals to Test and When
Most in the industry recognize that whole-herd testing is not practical or cost-effective. Instead, a systematic screening protocol devised with your veterinarian can be a more effective means to identify any persistently infected (PI) animals in the herd.
A starting point to determine if BVD is circulating within the herd is typically to test the calves in the herd. This BVD screening should be conducted at least 30 days in advance of breeding to avoid exposure of a pregnant cow by a PI animal. Because PI animals can have a negative impact on all the calves surrounding them, they should be removed from the herd and euthanized as soon as discovered. With this strategy, keep in mind that:
√ Individual identification is critical to match all samples with the animal tested and match the calf with its dam.
√ Cows do not need to be sampled and tested unless they have a positive PI calf. In the case of a PI calf, the cow should be identified, sampled and tested.
√ If an animal tests negative for BVD-PI status, there’s no need to ever retest that animal.
Additionally:
√ Consider testing replacement heifers prior to breeding as they prepare to go into the herd.
√ Purchased bred heifers or cows with an unknown BVD-PI status should be kept separate from the resident herd until their
√ PI status can be confirmed. Calves from these animals should be screened prior to commingling.
√ Bulls (and semen) should be purchased as BVD-PI free. If not, bulls should be screened prior to breeding season.
Producers may want to test every year for a few years. If no PI animals are being identified after a period of time, you may move into more of a monitoring mode by remaining vigilant about any unusual health problems or aborted fetuses, and include biosecurity and vaccinations as a regular part of herd-health protocols.