Bovine Viral Diarrhea in Cows: Signs, PI Calves, and Prevention
- See your vet immediately if cattle have fever, mouth ulcers, sudden diarrhea, abortions, weak calves, or a herd outbreak of respiratory or reproductive problems.
- Bovine viral diarrhea virus, or BVDV, can cause mild illness, severe mucosal disease, infertility, abortion, and immune suppression that opens the door to pneumonia and scours.
- Persistently infected, or PI, calves are the key long-term source of spread. They form when a fetus is infected early in gestation before its immune system can recognize the virus.
- Diagnosis often relies on ear-notch antigen testing or PCR, plus herd-level testing and repeat testing when needed to separate transient infection from PI status.
- There is no single antiviral cure. Care focuses on isolation, fluids, anti-inflammatory support when appropriate, treatment of secondary infections, and removing PI animals from the herd plan.
What Is Bovine Viral Diarrhea in Cows?
Bovine viral diarrhea, often called BVD, is a contagious viral disease of cattle caused by bovine viral diarrhea virus, a pestivirus. Despite the name, diarrhea is only one possible sign. Some cattle have mild or no obvious illness, while others develop fever, mouth lesions, pneumonia risk, reproductive loss, or a severe form called mucosal disease.
One of the most important parts of BVD is the persistently infected (PI) calf. A PI calf is created when a pregnant cow is infected early in gestation, usually around day 42 to 125 of pregnancy. The fetus may survive, but because its immune system is still developing, it may treat the virus as normal and shed large amounts of virus for life.
That is why BVD can be both an individual-animal problem and a herd problem. A single PI calf can quietly spread virus to penmates, pregnant cows, and replacement animals. In many herds, the biggest losses come from reduced fertility, abortions, weak newborns, and more respiratory disease rather than dramatic diarrhea alone.
Your vet can help sort out whether BVD is affecting one sick animal, a calf group, or the whole herd. That distinction matters because testing, isolation, and prevention plans are different for each situation.
Symptoms of Bovine Viral Diarrhea in Cows
- Fever and depression
- Diarrhea or loose manure
- Nasal discharge, cough, or pneumonia outbreaks
- Mouth ulcers, drooling, or erosions on the nose
- Poor growth, chronic ill-thrift, or repeated sickness
- Abortions, infertility, early embryonic loss, or weak calves
- Sudden severe diarrhea with dehydration and death
See your vet immediately if you notice mouth lesions, severe diarrhea, dehydration, abortions, multiple sick calves, or a sudden spike in respiratory disease. BVD can look like other serious cattle diseases, so testing matters. Herd-level clues are often as important as individual signs, especially if you are seeing repeat pneumonia, poor conception, abortions, or weak newborn calves.
What Causes Bovine Viral Diarrhea in Cows?
BVD is caused by bovine viral diarrhea virus (BVDV). Cattle usually become infected through direct contact with infected animals, especially nasal secretions, saliva, manure, urine, reproductive fluids, and contaminated equipment. The biggest source of spread is usually a PI animal, because that animal sheds virus continuously rather than for a short time.
Pregnant cattle are a special concern. If a cow is infected early in pregnancy, the fetus may die, be aborted, be born weak or malformed, or become persistently infected. Cornell notes that exposure around 60 to 125 days of gestation can produce a PI calf, and PI cows always produce PI calves.
BVD also moves through cattle traffic and management gaps. Purchased replacements, show animals, commingled calves, shared trailers, and contaminated clothing or equipment can all bring virus onto a farm. Semen and embryo-related biosecurity also matter, which is why herd prevention plans often include sourcing controls.
Not every infected cow becomes severely ill. Some have a short-term, or transient, infection and recover. Others, especially PI calves or cattle with secondary infections, can become much sicker. Your vet can help determine whether the main issue is acute infection, a PI animal, or a broader herd biosecurity problem.
How Is Bovine Viral Diarrhea in Cows Diagnosed?
BVD cannot be confirmed by signs alone because it can resemble other causes of diarrhea, mouth lesions, abortion, or respiratory disease. Your vet will usually combine the history, age group affected, pregnancy losses, vaccination status, and herd pattern with laboratory testing.
Common tests include ear-notch antigen capture ELISA, PCR, virus isolation, and in some situations serology. Ear-notch testing is widely used to identify PI cattle, especially calves and replacement animals. Cornell and other diagnostic labs also describe pooled and individual testing strategies for herd screening.
A positive result does not always answer every question on the first try. PCR can detect virus in transiently infected cattle, while some antigen-based ear-notch tests are especially useful for PI screening. When results are unclear, your vet may recommend repeat testing after a few weeks, testing cohorts, or testing the dam and calf together.
If a PI animal is found, the next step is usually herd investigation rather than stopping at that one result. Your vet may recommend testing purchased animals, newborns, exposed groups, or pregnant cattle depending on how the herd is managed.
Treatment Options for Bovine Viral Diarrhea in Cows
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Immediate isolation of suspect cattle
- Targeted PI screening with ear-notch ELISA or PCR, often $5-$30 per head depending on lab and pooling strategy
- Basic farm call and physical exam
- Oral or injectable fluids as directed by your vet for mild dehydration
- Nursing care, feed and water access, and close temperature and manure monitoring
- Removal from breeding or sale channels until status is clarified
Recommended Standard Treatment
- Farm call, exam, and treatment plan from your vet
- Diagnostic confirmation with ear-notch testing, PCR, and selective repeat testing
- Anti-inflammatory treatment and fluid therapy when appropriate
- Treatment of secondary bacterial pneumonia or enteric disease if your vet suspects it
- Testing of close contacts, dams, calves, or purchased replacements
- Isolation and herd biosecurity review, including vaccination timing and animal movement
Advanced / Critical Care
- Intensive treatment for severely dehydrated or recumbent cattle
- IV fluids, repeated monitoring, and advanced supportive care
- Full diagnostic workup for complicated outbreaks or valuable breeding stock
- Necropsy and laboratory submission for deaths to clarify herd risk
- Whole-herd or strategic surveillance testing, tracing, and PI elimination planning
- Detailed reproductive and biosecurity review with your vet and herd consultants
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Bovine Viral Diarrhea in Cows
Bring these questions to your vet appointment to get the most out of your visit.
- Do these signs fit acute BVD, a PI calf, or another disease that looks similar?
- Which cattle should we test first, and should we use ear-notch ELISA, PCR, or both?
- If one animal tests positive, which groups, dams, or penmates should be screened next?
- Do any positive animals need repeat testing to tell transient infection from persistent infection?
- What isolation and movement steps should we start today to protect pregnant cows and calves?
- How should we handle confirmed PI animals and their offspring within our herd goals and budget?
- Is our current vaccination program timed well enough to protect breeding animals before pregnancy?
- What is the most practical prevention plan for purchased replacements, show cattle, and returning animals?
How to Prevent Bovine Viral Diarrhea in Cows
Prevention starts with one core idea: keep PI animals out of the herd and protect pregnant cattle from exposure. Cornell's BVD control procedures recommend testing purchased animals for PI status, culling PI animals and their offspring, and using a structured vaccination program. Closed-herd practices, quarantine for incoming or returning cattle, and clean transport and equipment also matter.
Vaccination is helpful, but it is not a stand-alone fix. Your vet may recommend a modified-live or killed BVD vaccine program based on breeding status, age, and herd management. Timing matters because breeding animals need protection before pregnancy, and modified-live products are not appropriate in every situation.
Testing strategy is where many herds gain control. Ear-notch screening of calves, replacements, or purchased animals can identify PI cattle before they spread virus. Some herds also use pooled testing approaches to lower the cost range of surveillance, then follow up positives with individual testing.
Work with your vet on a written herd plan that covers vaccination, testing, quarantine, breeding management, and what to do if a positive animal is found. BVD prevention is usually most successful when it is treated as a herd systems issue, not only a sick-calf problem.