When Lucy Rechel analyzed all the cattle doctoring she was doing each fall, she found bovine viral diarrhea (BVD) was the biggest culprit. So the owner of Snyder Livestock, a 4,000-head-capacity cattle development center in Yerington, NV, laid down the law this year — all cattle destined for her facility must be tested and prove negative for the BVD virus before she'll take delivery.
“My intent is to have everyone test, then remove, persistently infected animals 30 days before shipping,” she says. “Of course, persistent infection is the most difficult part to control, but hopefully, they'll understand the hazard of keeping the persistently infected animal and will want to get it out of the herd.”
Her decision became a little less painful after she'd heard of a relatively affordable and reliable test used to identify cattle persistently infected (PI) with the BVD virus. The “ear notch” test developed several years ago at the University of Nebraska is now a standard for BVD diagnosis.
The Real Culprit
For help with her BVD eradication plan, Rechel gathered all the information she could from Bill Kvasnicka (Kwas-niska), Extension veterinarian, University of Nevada, Reno.
“A person like Lucy has to resort to this kind of program because 70-90% of all BVD infections occur without the appearance of clinical signs,” Kvasnicka says. “The real culprits are PI animals that remain infected for life. They shed huge amounts of virus and are primarily responsible for keeping BVD in a herd — and introducing the disease into other herds.”
Around 1993, it was determined that BVD is actually two diseases — BVD Type 1 and BVD Type 2. Both are caused by related, but separate, species of pestivirus.
“BVD viruses undergo mutation or continuous change,” Kvasnicka adds. The result is the existence of several strains within each BVD type and new strains being created in nature at anytime.
Emerging data about BVD indicates infection with Type 2 virus species often causes a more severe disease outcome than infection with Type 1 virus species.
BVD also suppresses the immune system, lowering an animal's disease resistance. As a result, other organisms can more easily infect animals, resulting in greater than expected problems with things like scours and pneumonia, according to Kvasnicka.
With this information and more under her arm, Rechel proceeded.
Feedlot morbidity wasn't Rechel's only concern. She'd heard some of her customer's heifers were aborting, presumably due to the BVD virus.
“If we're going to be in the business of developing and breeding heifers, I need to be sure that if my customers don't already have BVD in their herds, they aren't going to get it by bringing cattle to my feedlot,” she adds.
This year, Rechel has about 140 bulls consigned for her formal performance evaluation, and another 1,500 bulls and 2,000-2,500 heifers being developed for ranchers around Nevada and California.
More Questions Than Resistance
While Rechel might be among those leading the way in BVD biosecurity, not all her customers agreed with her new policy.
“I'm getting some people who say that if they're required to test for BVD, they won't be bringing cattle to me,” she says. “I was expecting some of that. But, I'm getting a lot more questions and interest than resistance.”
Charlie Hone, Garnerville, NV, is one consigner who's doesn't mind the new policy. He's a seedstock and commercial producer who routinely sends both bulls and heifers to Snyder Livestock for performance test and development.
“In the end, it'll save us all money,” he says. “I vaccinate for BVD anyway — but this is added insurance that we're not going to bring anything home that we don't want.”
Plus, he says, he can see where the increased biosecurity might induce more buyers to come to Snyder's annual performance sale.
“I can't see where it's anything but a good idea, as long as everyone is treated the same,” he says.
Rechel says she expects to see a 30-40% reduction in sickness the first year by keeping BVD out of her facility. “I hope it's more of a reduction, but there's no question we'll be treating fewer calves for BVD and its complications.”
A System Of Management
Helping Kvasnicka draft Rechel's plan was Julia Ridpath, a PhD microbiologist at the USDA/Agricultural Research Service (ARS) National Animal Disease Center in Ames, IA. She's the lead ARS scientist in the detection and control of BVD.
Ridpath says while foot-and-mouth disease and bovine spongiform encephalopathy have been getting all the attention, the U.S. cattle industry needs to now address BVD from every angle.
“Producers who are serious about controlling BVD should be vaccinating, combined with a surveillance and testing program specified by their field vets,” she comments. “There's no vaccine alone that's going to get rid of it, and no diagnostic test that will make it go away. … To control BVD, every rancher will have to learn as much as they can about BVD and develop a system of management.”
While some in the veterinary research community have been critical of BVD vaccines, Ridpath says there's generally more confidence in BVD vaccines today than a few years ago.
“The old data indicated that Type 1 vaccines didn't offer full protection against Type 2 field viruses,” she says. “The jury isn't totally ‘in’ on that though, but we're hoping things will get better now that we have both Type 1 and Type 2 antigens available to producers.”
She emphasizes that some BVD vaccines have both Type 1 and Type 2 “protection” listed on the product label, but some don't contain both antigens within the product.
“What they've done is taken the old antigen, tested it against Type 2 strains of the virus and said there's cross-protection,” she explains. “We know they are cross-reactive — we just don't know if that cross-reaction offers the kind of cross-protection a producer expects.”
Preventing Fetal Infection
Another problem with some BVD vaccines is that they're tested and licensed based on the prevention of the acute form of the disease as opposed to prevention of PIs.
“Often, the producer isn't thinking about the acute form of the disease — he's thinking about fetal protection,” she says. “Just because a vaccine reduces the acute disease in an animal, it doesn't mean you have prevented fetal infection.”
In order to stop fetal infection you have to completely stop viral replication, Ridpath says.
“Right now, we have vaccines that will help. But we don't have vaccines that will stop fetal infection 100% because there's so much variation in those viruses,” she says. “A rancher who expects total protection will be upset with a vaccine that gives them any PIs at all.”
Reproductive status also plays a role in how well BVD vaccines work. For instance, the immune system doesn't work quite the same in a pregnant animal as a non-pregnant animal, Ridpath adds.
Because the BVD virus is so widespread, Kvasnicka says most cattle herds are at risk for infection. He and Ridpath both say that emphasizing surveillance and biosecurity are critical to total BVD management.
“Ideally, newly purchased cattle should be vaccinated before entering the herd and isolated on the ranch or farm for two to three weeks,” Kvasnicka says. “Sick animals should also be quarantined to prevent the spread of infection.”
They say producers also can get into trouble by doing things like using colostrum from outside sources, buying calves to graft onto cows, purchasing groups of bucket calves, sharing stock trailers, or taking unvaccinated animals to cattle shows or the local 4-H fair.
Okay, so a rancher tests for BVD and identifies some PIs, what do you do with them?
Ridpath suggests one of two things:
Bite the bullet and eliminate them outright. “They certainly shouldn't be sold to someone else. Unfortunately, killing them might be the most cost-effective option in the long run.”
Feed the animals to market weight at home and get them processed without allowing contact with other cattle. The problem is that the PI that does well in the feedlot is a rarity.
While none of these steps in finding and eliminating PIs in a herd are simple or inexpensive, the alternative is to continue battling BVD on ranches and in feedyards, Ridpath says. Consequently, she applauds Rechel's approach to eliminating BVD from her feedlot and hopes others will follow suit.
“It can't help but make a difference when you have someone of Lucy's stature make that kind of commitment,” she explains. “Word will get around fast that some people are taking this disease very seriously and are willing to do something about it.”
For more information on BVD, check out www.beefcowcalf.com and click on Health and then Diseases.
“Dr. Bill's” Five-Step BVD Plan
Bill Kvasnicka, Extension veterinarian, University of Nevada, Reno, says bovine viral diarrhea (BVD) is a reproductive disease with immense economic consequence. It causes early embryonic losses, fetal abnormalities, abortions and the birth of persistently infected (PI) calves. He recommends the following procedures for ranchers to control BVD in their herds:
Step 1: Herd Diagnosis
Compile a complete and thorough herd history.
Identify five or more calves at branding and do not vaccinate them with a BVD vaccine. Collect blood samples of those calves at weaning to determine if BVD titers developed from branding to weaning.
Collect blood samples from five or more calves immediately after birth and before they nurse colostrum. Submit these samples for antibody titers. Detection of BVD titers indicates intrauterine infection, thus herd infection.
Submit aborted fetuses for virus isolation and collect acute and convalescing paired blood samples from aborting females to determine ascending BVD antibody levels.
Submit blood or necropsy tissues for virus isolation.
Have laboratory determine if infection is due to Type 1 or 2 BVD.
Step 2: Lower The Challenge
Ear notch all calves at branding to eliminate PI calves, plus ear notch the dam of any positive calves. Ear notch all open cows and the bull battery.
Step 3: Raise The Resistance
Have your veterinarian outline a vaccination program.
Utilize BVD vaccine as part of any pre-weaning or weaning vaccination program.
Include BVD vaccination as a component of a heifer development program.
Booster the cow herd yearly.
Time vaccination to ensure adequate resistance during the breeding season. Administer BVD and other reproductive disease vaccines 30-45 days before the breeding season.
It is important to realize that even if the cow is adequately vaccinated, the fetus may not be protected from infection
Step 4: Establish Biosecurity
Quarantine and test all herd replacements.
Don't buy calves to graft to a cow that has aborted.
Remember that testing pregnant replacement heifers requires testing their calves following calving.
Avoid grazing in common with herds of cattle that are not participating in a BVD eradication program.
Step 5: Herd Monitoring
Utilize 5-10 calves each calving season. Don't vaccinate these calves at branding, then collect blood for antibodies at weaning time, before pre-weaning or weaning vaccination.
Use these results as a sign of the unvaccinated calves' exposure during the time they're nursing. It indicates the dams were also exposed during breeding and gestation.
Blood samples also can be collected from newborn calves before they nurse to detect pre-colostral BVD virus antibodies indicating intrauterine infection during gestation.
For more information call Kvasnicka (Kwas-niska) at 775/784-1377 or e-mail [email protected]