Some veterinarians and producers think of bovine viral diarrhea virus (BVDV) in narrow terms – as the virus that causes persistently infected (PI) cattle. And while that perspective is correct, Dr. Thomas Passler, DVM, PhD, says there are broader implications for BVDV and its impact on cattle and some other animal species worldwide.
“(BVDV) has evolved over the years and is not a single virus or just a diarrhea-causing problem. Today it’s made up of three related viruses and 19 subtypes that cause similar diseases,” explains Passler, the Jack Rash professor of internal medicine for food animal medicine at the Auburn University College of Veterinary Medicine.
“It’s a sneaky, insidious disease,” he adds.
Passler estimates 0.5% of U.S. cattle are persistently infected by BVDV. Of that percentage, only a small number of those animals become PI cattle – a result of infection caused during fetal development between 40 and 125 days of gestation and which persists during the animal’s entire life.
The PI problem differs from transient infection (TI), which occurs when an animal becomes infected after birth. A TI animal is infected temporarily, but during that time is capable of shedding the virus and transmitting it to other herd members or pen mates.
Multiple Health Issues And Losses Across Species
BVDV-positive animals, especially PI cattle, significantly impact U.S. herds by causing immunosuppression, weakening immune systems and making herd mates more susceptible to other infections. Passler says that immunosuppression often manifests as increased calf death losses from diseases such as scours and pneumonia, as well as poor weaning weights.
Passler adds that he has seen similar problems from BVDV in other animal species, including hogs, white-tailed deer, alpacas and goats.
BVDV is one of the costliest bovine diseases for beef producers and dairy producers, as well. Losses average between $15 to $88 per head, conservatively, according to Indexx Laboratories, citing older data from 2002 and 2008.1-3
Despite the associated costs, a 2017 National Animal Health Monitoring System (NAHMS) study of 75 U.S. cow-calf producers (the summary was released in 2023) reported only 57.5% of participating producers said they knew some basics or were fairly knowledgeable about BVDV. In addition, 26.9% of producers said they “recognized the name but not much else,” and 15.3% of respondents said they had never heard of it (see Figures 1 and 2).
Furthermore, most BVDV infection problems in cattle herds go unnoticed since 70% to 90% of BVD infections are subclinical (do not result in observable disease), according to the Washington Animal Disease Diagnostic Laboratory.
Contributing Factors To PI Cattle
Direct contact with infected animals and with contaminated fomites (water buckets, calf feeders, feed bunks, IV equipment, etc.) are common ways BVDV gains a foothold in a herd.
One risk factor that often flies under the radar is the use of intranasal vaccines that do not address BVD viruses, reports Dr. Dan Thomson, PAC veterinarian and Iowa State University professor emeritus.
“We’re using a lot more intranasal vaccinations, thinking that we’re covering for BVDV when we’re actually not,” says Thomson, who spoke with Passler recently on an episode of DocTalk.
It’s a perspective Passler says he agrees with. “We see mucosal disease in the clinic – something we shouldn’t be seeing at all – and often from herds that vaccinate,” he adds.
Intranasal vaccines for respiratory disease do not currently contain BVDV Type 1 & 2, so a separate injectable BVDV vaccine is required, according to Craig A. Payne, DVM, and Celeste Morris, DVM, respectively, at the University of Missouri. Payne and Morris discuss this contributing factor further in their online article, Vaccination Program for a Cow-Calf Operation.
Key Into The Correct Timing To Test Calves
Payne and Morris recommend that “because PI animals are so detrimental, the standard recommendation in herds where BVDV is suspected is to implement a testing strategy and remove any PI animals detected. Vaccination alone cannot counter the effects PI animals can have.”
Specific to calves, Passler says it’s important for veterinarians to let producers know the timing of the testing can impact results – maternal antibodies can skew the results.
“Either test the calf as soon as it hits the ground, before it can nurse, or wait at least a week or [even up to] a month later,” he advises.
He encourages practitioners to talk with cow-calf producers about testing calves to identify BVDV.
“A lot of people don’t test until those animals are stockers or going to the feedlot, and that’s too late,” Passler says. “We want producers to test earlier so they can remove PI cattle sooner.”
Evaluate Vaccines And Protocols
There are two main types of vaccines for BVDV: modified-live (attenuated) and killed (inactivated).
The most significant value for beef producers in using a vaccine that addresses BVDV is being able to protect a dam’s fetus, Passler says. But no vaccine is perfect, he adds, noting producers must also be diligent with their management practices.
“What we have seen here in the clinic is that even in well-vaccinated herds – those we know use killed vaccines religiously – they still get PI cattle if they’re not careful about biosecurity,” he says. “These might be herds that religiously vaccinate, but they still go to the stockyards and buy replacements or take some other sort of risk.”
As for vaccine use protocols, Passler says his review of other researchers’ work indicates it’s best if producers use at least one modified live vaccine and then an inactive (killed) vaccine to vaccinate cows and heifers.
“I’d probably [vaccinate] two cycles and well before gestation, because vaccine seems to reduce fertility a little bit,” he says. “Some researchers say 42 days in advance [of gestation] is a good number to use”
Another practice Passler advises is using products from more than one manufacturer. “Different manufacturers use different vaccine strain viruses, so you might increase endogenic exposure,” he explains.
Thomson supports that recommendation. “We do that when we deworm, we do it with how we treat bacteria, so why wouldn’t we do that to prevent BVDV? That’s great advice,” he says.
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