You might remember what Lucy Rechel had cooked up when we visited with her last winter. She'd just required all her customers to start testing their cattle for the bovine viral diarrhea (BVD) virus before placing them in her feedlot.
The plan was designed to keep persistently infected (PI) BVD animals out of Snyder Livestock, her 4,000-head cattle development center (“Getting Serious About BVD” March BEEF, page 26) located near Yerington, NV.
“I was sick and tired of doctoring calves all fall,” she says. “We're convinced BVD was behind a lot of the sickness. We had to do something to address the BVD problem.”
Knowing that persistent infection is the most difficult component of BVD to control, Rechel made the decision after she learned of a relatively affordable and reliable test used to identify PI animals.
That PI-BVD diagnostic procedure came online in 1999 after University of Nebraska pathologists discovered that PI animals could be detected via a skin sample taken from a calf's ear soon after birth. Using immunohistochemistry (IHC) testing, the “ear notch” procedure is now a standard for PI-BVD diagnosis (see sidebar).
Working with her vet, Randy Wallstrum of Minden/Gardnerville, NV, Rechel developed an in-house protocol for taking and submitting ear notch samples for the virus. The test runs about $5/head for larger groups of cattle.
Has It Made A Difference?
“It's kind of hard to get a handle on the difference this program alone has made in the health of the individual herds we work with,” she replies. “This isn't the only change we've made, so there won't be a well-defined ‘before and after’ scenario.”
She says there has been an improvement in BVD awareness among her consigners and their vets, however. And consigners are doing more at home to prevent the disease.
“Detection and elimination of PIs isn't the only component in reducing BVD,” she explains. “Proper vaccination with the right products is the first step we try to relate to our customers.”
For some consigners, she feels her PI-BVD biosecurity program has made a huge difference.
“We had the easiest summer ever in terms of treating cattle. And we had less sickness in calves from some customers who traditionally have had more trouble,” she says.
She expects to see some evolving improvements in conception rates, especially in cattle from folks who don't get their heifers to the feedlot until a month or so before breeding.
“That's part of the awareness and understanding of the disease,” she says. “These folks know they'll have to test their calves ahead of time, so they're vaccinating, asking questions and generally paying more attention to BVD.”
But getting everyone to buy into the program hasn't been as easy as she hoped. “I thought that what we wanted to do was such a great idea that everyone would jump right on it,” she says. “But, I'm finding it's harder than I thought to buy in.”
Will Routine Testing Work?
Rechel's experience has made her wonder if routine testing for PI-BVD that works in a development center is practical for a commercial feedyard.
She's had some commercial feeding customers say they're not bringing calves to Snyder Livestock this year. But, she thinks that decision is more related to the current economics of retained ownership than her new biosecurity measures.
“With feeder prices like they are, most people with commercial feeder calves are deciding not to feed this year,” she says.
But, she's learning that even under a cattle development center concept, peer pressure can be an important tool in driving acceptance. And, as BVD gains more attention and biosecurity is stepped-up via testing, her purebred cattle customers are beginning to turn to PI-BVD testing as a marketing advantage.
For example, Silveira Bros., Mindota and Firebaugh, CA, began testing its Angus, Red Angus and Charolais bulls for PI-BVD as a result of Rechel's policy. They've since gone a step further.
In advertising their annual Partners For Performance sale, Silveira Bros. promote the “extra guarantee” of their bulls being PI-BVD negative and vaccinated for Types 1 and 2 BVD viruses, along with being preconditioned for 45 days.
“PI-BVD testing is one of the most beneficial things we can do collectively as an industry,” says Darrell Silveira. “And now, with Lucy's program, we tell our customers that our bulls have been kept in a facility where the other animals have also been tested.
“Lucy got us started,” Silveira says. “I think this kind of thing is going to force at least everyone who sells breeding stock to begin testing for PI-BVD.”
The Best-Case Scenario
As Rechel's consulting vet, Wallstrum says BVD testing is only one of the innovative steps she's initiated.
“Things ‘happen’ with Lucy — it's a pleasure to work with her,” says Wallstrum. “She's done a lot to help her customers develop and exhibit the various traits in their cattle, but this testing program was a courageous step.”
He says the jury is still out on the amount of sickness and death loss they've been able to prevent. But, he says he's “cautiously optimistic” they won't see the “breaks” in sickness they've experienced in the past.
“I'm convinced this program will reduce the odds we'll have the kind of problems associated with BVD we've seen in the past,” he says.
Both Rechel and Wallstrum point to Bill “Dr. Bill” Kvasnicka, retired University of Nevada-Reno Extension veterinarian, as the real guru behind the methods used to quarantine BVD from Snyder Livestock.
“Dr. Bill is the real brains here,” says Wallstrum. “He's the scientist — Lucy and I just do what he suggests. It's a great team.”
What does this BVD team see as the best-case scenario for BVD control?
First, Rechel is adamant in recommending ranchers work closely with vets intimately familiar with BVD and the interactions surrounding PI. That said, she's all for aggressive vaccination and testing.
“The best thing would be for ranchers to test calves for PIs at birth,” she says. “Then couple that with vaccinating open cows with a modified-live virus (MLV) vaccine and their calves at branding with an MLV.”
New Brand Of Biosecurity
Kvasnicka says that until recently he couldn't advocate vaccinating calves at birth. It's long been believed that maternal antibodies inactivate or interfere with vaccine, he says.
But recent USDA research shows calves vaccinated with MLV BVD virus developed BVD virus Type 1- and Type 2-specific T-cell responses in the presence of maternal antibody. “Now we know vaccinating with a MLV vaccine at branding will stimulate the immune system in the calf,” Kvasnicka says.
This is important because 90% or more of PI calves die before weaning.
Wallstrum emphasizes that biosecurity must go way beyond “foot baths and clean clothes.” He says Rechel's brand of biosecurity is what's needed to get a handle on the various strains of the BVD virus.
“We don't have any idea how much biosecurity is necessary to stop the spread of the BVD virus,” agrees Kvasnicka. “Right now, Lucy is doing way more than most feeders. She's doing some things that should be taken as an example of what can be done to control this disease.”
Academy Of Vet Consultants' BVD Control Guidelines
Though the bovine viral diarrhea (BVD) virus can be transmitted across fences and by commingling livestock, the main infection source is persistently infected (PI) animals. These animals are produced as a result of infection of the fetus during days 30-145 of gestation — before the fetal immune system has developed enough to recognize the virus as foreign. Thus, a carrier PI animal results and sheds the virus throughout its life.
Several diagnostic tests are available to determine the presence of BVD virus in a herd. Serological testing of blood samples has limitations due to confusing titers from vaccinations. Virus isolation (VI) can be quite specific, but it's more costly and requires more lab time.
Immunohistochemistry (IHC) on a skin biopsy or ear-notch is reliable and cost-effective in identifying PI calves. Up to 1% of calves are born PI. This test can be done shortly after birth and provides assurance that calves aren't virus shedders.
Quarantining new animals before moving them into the herd allows time for diagnostic testing to determine the presence of virus or PI. Quarantine allows animals to be properly immunized in accordance with a herd health plan.
This past July, the Academy of Veterinary Consultants (AVC) adopted a set of BVD surveillance strategies to determine the level of risk for the presence of PI animals in a herd — high risk vs. low risk. Those AVC recommendations include:
In High-Risk Herds
“High risk” herds should utilize whole-herd screen tests to identify and eliminate PIs. High-risk includes herds with poor reproductive performance or high calf mortality and morbidity that can't be attributed to other management factors. A herd is also considered high risk if there's any laboratory confirmation of BVD transient or acute infection or PI animals.
In those cases, AVC recommends testing all cattle for presence of PIs before the breeding season:
For calves of all ages the (IHC) test is appropriate.
For cows without calves (open or calf died) use an IHC, Ag Capture ELISA, VI or pooled polymerase chain reaction (PCR) blood test.
For replacement bulls and heifers (purchased or raised) use an IHC, Ag Capture ELISA, VI, PCR test.
Animals that test positive for BVD virus are safe for human consumption and should be sold for slaughter. AVC says mothers of calves testing positive should be tested and:
All cows pregnant at testing time must be removed from the breeding herd as the fetus' BVD-PI status is unknown.
Absence of confirmed PI calves doesn't guarantee absence of a BVD problem. If still suspicious, test your next calf crop.
Implement a complete vaccination program prior to breeding in replacement animals and appropriate boosters in adults.
Prevent direct contact with cattle of unknown BVD status.
In Low-Risk Herds
For herds with a good reproductive performance history and showing no evidence of acute or transiently infected or BVD-PI animals, surveillance is key.
Continually monitor stillbirths, neonatal morbidity and mortality and weaning percent.
Routinely necropsy abortions, stillbirths and mortalities. Submit samples for analysis.
AVC also suggests ranchers consider a surveillance strategy involving pooling of 20-30 blood samples/100 head using PCR testing to screen for PIs.
Test calves before the breeding season.
A positive PCR test doesn't differentiate between acute BVD infection and PI animals. Therefore, the herd manager must do other confirmatory testing using IHC in suspect groups.
The IHC skin sample test can be used in a high-cost/high-sensitivity strategy on the entire calf crop to identify PIs before breeding. But, the operator must be sure to confirm positives in herds with no prior evidence of PIs.