Bovine viral diarrhea (BVD), caused by the bovine viral diarrhea virus (BVDV), is one of the cattle industry’s most economically important diseases. Despite its name, diarrhea is rarely the defining feature of the disease. Instead, BVD quietly undermines herd health by suppressing the immune system, contributing to reproductive losses and increasing susceptibility to respiratory disease and other infections.
Because many infected animals appear healthy, misconceptions about the disease can leave costly gaps in prevention and control programs. Vaccination, diagnostic testing and strong biosecurity all play important roles, but no single tool is enough on its own. Here are five common myths about BVD and the facts producers and veterinarians should know.
Fiction #1: The most common symptom of BVD is diarrhea.
Fact Check
The name bovine viral diarrhea may be misleading. In reality, diarrhea is a relatively uncommon symptom of the disease. BVD is primarily a reproductive and respiratory disease, with early signs of more virulent infections often resembling influenza, including fever and depression. Oral ulcers, particularly on the hard palate, along with nasal discharge, may also be observed.
When asked about the name of the disease, Dr. Robert Larson, Kansas State University veterinarian and professor, said: “It’s kind of unfortunate because diarrhea is actually relatively uncommon, but when it first showed up in the 1940s, it was. So it must have mutated. Diarrhea was a significant and obvious clinical sign that didn’t last long.”
He suggests that changes in the virus, or adaptation of the cattle population, likely contributed to the shift in clinical presentation.
Fiction #2: Vaccines aren’t a great tool against BVD.
Fact Check
Vaccination remains one of the most effective tools for reducing the impact of BVD and is a routine component of most herd health programs. Vaccines help protect against reproductive losses in breeding animals and reduce respiratory disease in growing cattle. However, Larson cautions that vaccination alone cannot eliminate the disease.
“The vaccines are actually pretty helpful at reducing the risk of abortion in a cow group. And in stocker and feedlot cattle, they’re pretty effective at reducing the risk of respiratory disease. But they’re not good enough to control the disease with vaccines only,” he says.
The biggest challenge is the persistently infected (PI) animal. If a pregnant cow becomes infected between approximately 60 and 120 days of gestation, the developing fetus may become immunotolerant to the virus and be born persistently infected. These calves shed large amounts of virus throughout their lives, continually exposing herdmates.
“Sometimes when we discover a few of these PI calves, they are in a vaccinated herd. So the vaccine has kept it from being obvious, where it provides some level of protection to the cattle so that they don’t look sick, but there’s still some PI animals in there,” Larson says. “The vaccines are actually pretty decent, but I don’t want to oversell vaccines. They always leave a window of opportunity, those PI calves.”
For that reason, vaccination should be paired with diagnostic testing and surveillance, particularly when reproductive losses or respiratory outbreaks raise suspicion of BVD.
It is also important to recognize not all vaccines are identical. There are at least two major viral genotypes circulating in North America, each containing multiple subgenotypes. Vaccine protection can vary depending on which strains are included.
“In North America, we have genotypes 1 and 2, and then the basic subtypes we have of Type 1 are A and B,” explains Dr. Christopher Chase, South Dakota State University veterinarian and professor emeritus. “The thing is, there are some Type 1A vaccines that give you good protection against 1B, and some that don’t.”
Because predominant strains can shift over time and vary by region, veterinarians should consider local disease patterns when developing vaccination protocols.
Fiction #3: BVD diagnostics aren’t worth your time.
Fact Check
According to Larson, today’s diagnostic tests are highly reliable and are essential for identifying the animals responsible for maintaining BVD within a herd.
“Our diagnostic tests for this disease are quite good,” he says. “When we work up a case using diagnostic tests, what we’re really asking is ‘Help me find all the persistently infected animals on the farm.’”
PI cattle carry extremely high concentrations of virus in their tissues. While blood and fecal samples can be used, ear-notch testing has become one of the preferred methods because viral levels in skin are exceptionally high in PI animals.
Using the same ear-notching tool commonly used in swine, veterinarians can collect a small tissue sample for laboratory testing.
“If it’s a persistently infected animal, that skin will be just loaded with the BVD virus. If it’s a temporarily infected animal, I’d expect none or a few viral particles in the skin,” Larson explains. “It’s not only ‘Yes, they have BVD’, but ‘Yes, this is a persistently infected animal.’”
Accurate diagnostics allow the identification and removal of PI animals before they continue spreading virus throughout the herd.
Fiction #4: If my herd is BVD-free, I’m good to go.
Fact Check
Successfully eliminating BVD from a herd is a major accomplishment, but it doesn’t mean the job is finished.
“If you have eliminated BVD from your herd, unless you’re living in a castle, you still need to keep testing,” Chase says. “The usual way the virus gets into a herd is through transient infection. If you’re buying bred animals, there’s no way to know for sure whether or not that calf in utero is persistently infected or not until it’s born. We don’t have a good test for that.”
Completely closed herds are uncommon. Dairy operations routinely add replacement animals, while beef producers may use community pastures or introduce outside cattle. Wildlife, including white-tailed deer, can also carry BVD.
The overall risk depends on management practices, but it is never zero. Continued surveillance and thoughtful biosecurity remain important even after a herd has achieved BVD-free status.
Fiction #5: Animals can become persistently infected at any stage of life.
Fact Check
Unlike many infectious diseases, cattle cannot become persistently infected with BVD after birth. PI animals are created only when infection occurs during a specific window of fetal development.
“It’s one of the reasons why we have good control programs for this disease,” Larson says. “An animal can never change their test status. If they test positive, they’re positive for all their life. If they test negative for persistently infected status, they’re negative for all their life.”
Although PI calves often experience poor growth, increased susceptibility to disease and shortened lifespans, identifying these animals provides one of the greatest opportunities for disease control. Because PI cattle continuously shed virus throughout their lives, removing them from the herd dramatically reduces viral transmission and helps protect the health of the remaining animals.
Five Keys to BVD Control
While no single management practice can eliminate BVD risk, combining several proven strategies can dramatically reduce the virus’ impact on herd health.
1. Vaccinate strategically. Vaccination remains one of the best tools for reducing reproductive losses and respiratory disease, but it should be viewed as one component of a comprehensive BVD control program rather than a standalone solution.
2. Identify and remove PI animals. PI cattle are the primary source of virus transmission within a herd. Finding and removing these animals is one of the most effective ways to reduce disease spread.
3. Use diagnostics when BVD is suspected. Modern diagnostic tests are highly accurate and can help identify PI animals before they continue exposing the rest of the herd.
4. Maintain biosecurity. Even herds that have successfully eliminated BVD remain vulnerable to reintroduction through purchased animals, community grazing situations and wildlife reservoirs. Ongoing surveillance and thoughtful biosecurity help reduce that risk.
5. Work as a team to develop a plan. Every herd has different management practices and disease risks. Developing a vaccination, testing and biosecurity plan provides the best opportunity to keep BVD from gaining a foothold in the herd.
