Your cow-calf clients have tested or are beginning to test their herds for persistently infected (PI) bovine viral diarrhea virus (BVDV) calves and their dams. Some may have found PIs and culled them from the herd. Others may have found no PIs and are now satisfied that they have no BVDV problems. So where do they go from here?

This is where some veterinarians are finding themselves in a Catch-22 with their clients. Many producers feel if they have no PIs, or have eliminated PIs, their herds are safe and secure. Others, armed with information from ear-notching calves, aren’t sure what their best options are for monitoring the virus in the herd as they go forward.

Phillip Kesterson, DVM, Western Livestock Consulting, Bridgeport, Neb., is in his second year of working with clients on BVDV programs. “We started testing the first herds in 2003 because of suspected problems or because of progressive producers who decided to voluntarily test based on economics and the availability of new testing methods,” Kesterson says. The most obvious problems, he notes, were illness and death loss of the calves that were retained in the feedlot.

Where to go from here is what Kesterson is now contemplating.

Set goals first
But, before you design surveillance strategies, you need to sit down with your producers and talk. “Discussing the goals for the herd is a critical first step before beginning BVDV surveillance,” says Dave Smith, DVM, PhD, Dipl. ACVPM, University of Nebraska. “For some herds, surveillance may cost more than the disease or because the producer or veterinarian is not committed to other components of BVDV control, such as biosecurity or biocontainment.”

Kesterson basically took the BVDV guidelines from the Academy of Veterinary Consultants and others and started by asking his clients what their goals, objectives and plans were, and what they were willing to do. “We showed them how we get from A to B on a case-by-case basis. It’s very important for veterinarians to know the clients’ goals.”

Complacency is also an issue. “Test results will be misinterpreted or misused,” adds Smith. “Not finding BVDV doesn’t mean that biosecurity can be relaxed.” Surveillance only indicates the current status of the herd and the results may not be predictive of future problems.

In particular, Smith worries that herd owners may let down their guard after eliminating BVDV from their herds. “Several models of BVDV control suggest that clinical signs of disease with re-exposure are likely to be more severe after the herd has lost the immunity that comes with ongoing exposure.”

Kesterson feels the same way. “There are producers who voluntarily become passionate about this issue, and they will stay at the forefront of testing and surveillance. Producers in the middle, if they test negative, may assume for many years that they are safe. I don’t know what I’m going to do with those clients.”

One of Kesterson’s clients who did a complete herd test last year is going to test again. “We discussed what can happen with BVDV, how good the test is, that we believe we found all PIs and we vaccinated, but could BVDV sneak back in? The client’s perception is that the value, not the cost, of the test is worthwhile, and that’s worth more to him than having the risk of BVDV.”

Steve Strubberg, DVM, Hermann Veterinary Clinic, Hermann, Mo., says he also deals with complacency in his smaller herds of 30-100 cows. “Monitoring in these few herds ranges from no further testing to some surveillance testing, including dam if known,” he says. “We usually step up the vaccination program for a while, but some have let the control measures slip due to lack of further disease.”

Assess risk factors
The problem with testing and finding out a herd has no PI BVDV animals is that producers may disregard ongoing risk factors, such as the one bred heifer that gets purchased and introduced into the cow herd, the new bull of an unknown disease status and even the neighbor’s herd that might not be vaccinating or testing.

“I don’t know of anyone I work with that has a closed herd,” says Kesterson. “There are people that think they do, but if you start asking them questions. they light up and say they forgot about certain things.”

Because of that, Kesterson talks to clients about their least-controllable risk factors, such as fenceline contact and the reality of cattle becoming commingled on the range. “Controllable factors are vaccinating and testing herd additions, but fenceline contact is the wildcard in this area.”

Kevan Albertson, DVM, Stockman’s Veterinary Clinic, North Platte, Neb., agrees and encourages clients to find out when other neighbors with cattle of unknown disease status are grazing pastures adjacent to theirs.

In cattle country, most producers generally know what type of programs their neighbors are on – whether they have well-vaccinated herds or are dealing in sale barn cattle of unknown origin. Kesterson tells clients there are producers out there who aren’t as well-protected as they may be and are at a higher risk. “I tell them we have to assume those cows can get in with theirs.”

In his smaller herds, Strubberg says many producers bring in animals with unknown backgrounds, and neither test nor quarantine them. A few of his good producers limit new arrivals and buy bulls from reputable sources, but even they are rarely tested.

Other management factors, such as intensive rotational grazing, can influence disease spread. Albertson says herds using an intensive rotational grazing system with high animal density during the breeding season can have a higher exposure to circulating infectious agents than they would on larger tracts of land. “In those herds where the disease challenge is high, we recommend a yearly booster of modified-live BVDV vaccine at least 30 days prior to breeding,” he says.

Protect original herd
In BVDV-endemic regions, vaccination may be more important to herds without BVDV than to infected herds, says Smith, as the cattle herd becomes progressively naïve to BVDV after the virus has been eliminated. Protection from severe clinical signs is gradually lost as fewer and fewer animals have immunity to BVDV. Several models of BVDV control predict that severe clinical signs of disease are more likely following re-exposure to the herd that has eliminated the virus. “In the United States, the risk is high for BVDV exposure from neighboring herds, purchased replacements, etc.,” notes Smith. “There, it is especially important to use vaccination to maintain a level of herd immunity in herds without BVDV.”

To a non-infected herd, probably the biggest threat is replacement animals and PI calves born into the herd. Therefore, it is extremely important that the main herd, especially pregnant cattle, not be exposed to calves conceived somewhere else. “Replacement heifers should calve in isolation until the calf is BVDV-test negative, but unfortunately this can be difficult for many producers,” says Smith.

In east-central Missouri where Strubberg practices, it’s recommended that incoming animals are ear-notched and quarantined, but, “the majority of our herds ignore these recommendations,” says Strubberg.

In Kesterson’s herds that have been tested and PIs eliminated, any bred replacement heifers that were introduced were ear-notched on arrival and quarantined until results were negative. Management on those operations didn’t allow for those heifers to be kept in quarantine until calving, so those calves were tested at branding before bulls were introduced into breeding pastures.

For those herds that tested in 2003, this year Kesterson is selecting a subset of the animals to test. “We’ve skipped our traditional branding vaccination and have bled those animals and frozen the serum, then we’ll do a second blood test to see if there is a change in titer suggestive of natural infection in the event we have any PI calves left in the herd.”

Protect new additions
New additions are a threat to the herd, but new, naïve animals can also be threatened by the home herd themselves. “In a lot of the Sand Hills herds, we may have some circulating BVDV virus, and our emphasis is not only protecting the cow herd against new herd additions, but also protecting the new herd additions against the cow herd that might have endemic BVDV problems,” says Albertson. “One of the biggest problems we have is adding naïve pregnant females to the main cow herd and then seeing BVDV abortions.”

Albertson also recommends if pregnant naïve females are added to the herd, that they be maintained as a separate herd for the first calving and breeding season. “This gives us time to properly test and immunize new additions.” After calving, the offspring born to new herd additions are tested for PI status, and the dams are vaccinated with modified-live vaccine at least 30 days prior to breeding.

 

Dave Smith, DVM, PhD, Dipl. ACVPM,  says discussing the goals for the herd is a critical first step before beginning BVDV surveillance.

Testing calves
The first herds Kesterson worked with screened all calves with ear-notching and immunohistochemistry between birth and branding. However, calves that didn’t make it between birth and branding were the unknown factor. “We tested all calves that were biological offspring, and if we had a non-biological pair, such as a grafted calf, we tested the dams.” (For a BVDV testing chart, see Practice Tips, page 56.)

Once a herd has tested calves, your client may or may not feel the need to test again the following year, depending on vaccination and biosecurity measures on the operation. Albertson says he is PI testing baby calves in herds that are suffering from production losses due to BVDV or where PI calves have actually been identified. PI calves are euthanized, and their dams are PI tested. PI dams are sent to slaughter. Those found to be PI-negative remain in the herd.

 

Necessary elements of a BVDV control plan involve elimination of PI animals in combination with a complete vaccination program, says Kevan Albertson, DVM.

“Many producers have improved their vaccination programs but have failed to eliminate PI animals already present within the herd,” says Albertson. “Those PI animals can shed large amounts of virus to the cow herd during the breeding season, creating more PI calves,” Albertson says. “Necessary elements of a BVDV control plan involve elimination of PI animals in combination with a complete vaccination program that will provide protection to the fetus.”

If you’re going to test large groups of calves or even a whole herd, Kesterson suggests calling your diagnostic lab ahead of time to schedule the testing. “It’s important if you are going to send large amounts of samples to let them know they are coming, so they can be ready and have the appropriate staff available.”

PI problems from ranch to feedlot
Persistently infected BVDV calves do not all die on the ranch. Many of them make it to the feedlot. This is why having a relationship with the feedlot where your clients’ calves are going can help you get information back to the ranch about often-preventable problems. “We don’t see a lot of clinical BVDV at the ranch,” says Albertson. “Many PI calves will appear healthy upon arrival at the feedlot and then die acutely or chronically at a later date.” Often knowing about these feedlot-level problems spurs Albertson’s clients to test baby calves back at the ranch.

 

Phillip Kesterson, DVM, says fenceline contact is the wildcard in the area of controllable BVDV factors.

Albertson encourages his feedlot clients to inform the original owners of PI calves that they have a BVDV problem so ranch-management changes can be made. One of Albertson’s feedlots had a customer from the Northwest who had eight out of 100 calves die from mucosal disease in the feedlot. As a result, Albertson put together a BVDV elimination and control plan for the producer. “We encourage our feedlot customers to provide complete health information to the producer if possible,” says Albertson. “Open communication between feeders and cow-calf producers is critical to the long-term success of the beef cattle industry.”        

The presence of PI calves in the feedlot will not only contribute to increased morbidity and mortality in their penmates but can adversely affect the health and performance in adjacent pens.

Because of retained ownership, Kesterson says those producers sending non-PI calves to the feedlot will gain a measurable benefit. “The irony of it is that the feedlot owner and the owners of the cattle in adjacent pens will benefit because the performance and health numbers will be better. The owners who didn’t test but have relatively clean herds will have a measurable benefit because of reduced exposure and subsequently reduced morbidity and possible mortality, so the benefit might actually be greater to your neighbors in the feedlot.”

Kesterson believes there are a lot of opportunities with clients based on what their goals are and what their operation means to them. “I think we have excellent tests, and if we as an industry would begin to use them and use them well, I think we could have a dramatic effect on the prevalence of BVDV.”

AVC BVDV Guidelines

For more information on the Academy of Veterinary Consultants’ BVDV Guidelines, visit  www.avc-beef.org and access the “links” page, then click on “Internet links.”

BVDV control program

Kevan Albertson, DVM, Stockman’s Veterinary Clinic, North Platte, Neb., offers his BVDV control program:

LOW-RISK HERDS

Herd history:

  • Normal herd production performance
  • Raise own replacement females
  • Purchase replacement bulls from reputable purebred herds that use biosecurity principles
  • Limited exposure to herds of unknown BVDV status
  • Production performance and individual records do not show any evidence of persistently infected (PI) animals in the herd (pregnancy rates, pregnancy loss percent, calf morbidity and mortality are within normal range)
  • Replacement heifers are on a complete vaccination program
  • Feedlot performance, morbidity, mortality are normal
  • Laboratory tests have shown no evidence of BVDV problems

Plans:
Maintaining herd immunity through vaccination and nutrition

  • Replacement heifers receive three doses of modified-live vaccine prior to first breeding
  • Vaccination is effective for controlling risk when exposure is present: vaccination does not prevent birth of all PI calves

Preventing effective contacts

  • Develop calving and breeding-management plans to reduce exposure
  • Minimize fence contact with herds of unknown BVDV status: establish cattle flow to minimize risk for exposure if fenceline contact is unavoidable

Prevent entry of BVDV into the herd

  • Test all purchased additions to the herd prior to entry

Herd monitoring

  • Herd testing and eradication plan is most likely not cost-effective
  • Monitoring will determine the BVDV status of the herd and what economic effect the virus is having on the herd
  • Monitoring will allow evaluation of BVDV control program
    a) Monitor individual and herd production performance and health
    b) Monitor feedlot performance
    c) Perform postmortem exams and test individual problem animals to determine if PI animals are in the herd
    d) If monitoring detects PI animals or if herd production declines because of suspected BVDV, implement a high-risk control and eradication plan

HIGH-RISK HERDSs

Herd history:

Decreased cow herd production performance

  • a) Increased calf morbidity, mortality, decreased weaning performance
    b) Decreased conception rates and increased pregnancy loss
    c) Postmortem exams and lab results have shown that PI animals are present in the herd

Plans:

Testing and removal of all persistently infected animals is the primary focus for effective BVDV control

  • Testing should include all calves born, all replacement heifers, cows without calves and bulls
  • Test the dams of positive calves
  • All positive animals should be removed from the herd prior to the next breeding season

Cow herd BVDV resistance needs to be improved through proper vaccination and nutrition

  • Replacement heifers receive three doses of modified-live vaccine prior to first breeding
  • Purchased and home-raised females receive a yearly booster of modified-live BVDV vaccine after calving
  • Establish a balanced cow herd nutrition program to improve pregnant cow and nursing calf immunity

Prevent effective contacts to minimize the economic effect that BVDV will have on the cow herd

  • Maintain low animal density: keep cattle spread out during calving and breeding
  • Decrease contact time: pair out quickly to large areas and clean ground at calving time
  • Minimize fence contact with herds of unknown BVDV status: establish cattle flow to minimize risk for exposure if fenceline contact is unavoidable

Prevent BVDV introduction into the herd

  • Eliminate contact with other herds
  • All herd additions need to be tested and isolated prior to entry into the herd
  • Purchased pregnant females need to be maintained as a separate herd for the first calving and breeding season
    a) Purchased pregnant females receive a modified-live BVDV vaccination after calving
    b) Calves born to all purchased pregnant females need to be tested for PI status
    c) Dams of positive calves need to be tested
    d) All positive animals go to slaughter
  • Purchased open replacement heifers need to be PI tested and vaccinated with two doses of modified-live BVDV vaccine before breeding the first time
  • Purchased bulls need to be tested for PI status before entry into the herd

Utilize a monitoring program after testing and removing PI animals

  • Monitor herd health and production performance
  • Monitor feedlot health and performance
  • Test BVDV suspect animals: perform postmortem examinations and do live-animal testing on suspect cattle

Using performance parameters

Evaluation of health and performance parameters is an important service veterinarians can offer to clients. “Health and performance records are also an important source of information for making decisions about BVDV control,” says Dave Smith, DVM, PhD, Dipl. ACVPM. “These records may provide the first evidence that BVDV is a problem in the herd. Also, they provide outcome measures useful to demonstrate the impact of a BVDV control program.

Kevan Albertson, DVM, believes that the only way veterinarians can help clients know whether BVDV programs are cost-effective is to help them develop recordkeeping systems to monitor production performance. He prefers the SPA-P program to track production losses through the whole management system. “My emphasis is on measuring production performance and evaluating if we have any production losses due to disease. If we need to take the next step in terms of diagnostic work, we can. But until we have a means for measuring losses, it’s very difficult for us to determine how cost-effective our recommendations are for producers.”

For his monitoring programs, Albertson starts with evaluating pregnancy rates. Nutritional status, breed, body type, fleshing ability, age, etc., determine what the pregnancy rate should be, which in Albertson’s herds is normally 93-98 percent. If pregnancy rate falls below what he feels is normal in a particular herd, he looks for nutrition problems, as well as infectious disease such as BVDV and trichomoniasis. “If we find stillborn calves and aborted fetuses, we’ll do paired serology on the cows and analyze fetal tissues.” After looking at pregnancy rate, he analyzes pregnancy loss. If it gets to be over about 2 percent, diagnostic work is in order.

Phillip Kesterson, DVM, also uses performance parameters to monitor herds on BVDV programs if they are not going to test in a given year. “We can continue serology, and watch the traditional production parameters, such as pregnancy rate, the number failing in the first cycle, abortions, stillbirths, calf heath issues. These are meaningful but not as accurate as testing.”

Albertson agrees that monitoring the health of baby calves is important. Large amounts of virus shed from PI animals within the herd can overwhelm herd immunity, the end result allowing secondary pathogens to produce respiratory and enteric disease in baby calves.