Bovine virus diarrhoea, commonly called BVD, is a contagious viral disease affecting cattle worldwide. It spreads through close contact in herds and can cause fertility problems, poor growth, and higher susceptibility to other infections.
Effective control combines vaccination, biosecurity, and regular testing to identify and manage persistently infected animals. Understanding the main drivers of transmission and persistence helps producers reduce losses and protect herd performance.
| Feature | BVD Virus Biotypes | Cytopathic Effect | Common Clinical Signs |
|---|---|---|---|
| Non-cytopathic (NCP) | Forms persistent infection in calves | Not detected in cell culture initially | Immunosuppression, diarrhoea, mucosal disease |
| Cytopathic (CP) | Can appear after superinfection of PI animals | Visible cell rounding and detachment | Acute severe diarrhoea, high fever |
| Strain diversity | Type 1 and Type 2 strains | Associated with disease severity | Reproductive failure, congenital defects |
| Transmission routes | In utero, direct contact, fomites | Persistence depends on gestational age | White blood cells carry virus long-term |
Persistent Infection And Foetal Impact
When a susceptible pregnant cow is infected with BVD virus early in gestation, the developing calf can become immunologically tolerant to the virus. This results in a persistently infected (PI) calf that continuously sheds high levels of virus, creating a major reservoir for herd transmission. PI animals often appear normal but may later develop mucosal disease under triggering conditions.
The outcome for the foetus depends on the stage of pregnancy at infection. Early infections tend to cause embryonic loss or congenital defects, while later infections can produce PI calves that survive but spread the virus silently. Identifying and removing PI calves is central to breaking the cycle of persistent infection within a operation.
Clinical Disease Patterns And Diagnosis
Acute BVD And Mucosal Disease
Acute BVD occurs when a non-immune animal encounters a cytopathic strain or is superinfected with CP BVD while already carrying NCP virus. This can lead to fever, severe diarrhoea, mouth ulcers, and a marked drop in milk yield. Mucosal disease is a frequently fatal end-stage that arises in PI animals when the virus mutates to a cytopathic form.
Subclinical Effects And Diagnosis
Many infections are subclinical yet still impair immunity and reproduction, making diagnosis dependent on laboratory testing rather than signs alone. Serology, antigen detection, and molecular assays help identify active infection, past exposure, and the presence of PI animals. Regular monitoring and clear interpretation of test results support targeted control strategies.
Herd Management And Biosecurity
Robust biosecurity reduces the risk of introducing BVD virus through new livestock, semen, or contaminated equipment. Isolation, pre-entry testing, and strict traffic control on farms limit the entry and spread of infection. Vaccination of breeding stock enhances protection but should be integrated with removal of PI animals to achieve long-term control.
Strategic vaccination protocols aim to protect pregnant cows and reduce the chance of persistent infection in calves. They also lower viral pressure in the environment, benefiting younger stock and improving overall productivity. Herd health planning should align vaccination and testing schedules with local epidemiology and farm-specific risks.
Economic And Herd Performance Impacts
BVD can significantly affect profitability through lost calves, reduced growth rates, treatment costs, and failed performance targets. Even low-level endemic circulation may suppress fertility, increase culling rates, and prolong the time to market for youngstock. Clear metrics around pregnancy rates, average daily gain, and treatment response help quantify the financial burden.
| Indicator | With Active BVD Circulation | Under Effective Control | Target Benchmark |
|---|---|---|---|
| Calving rate | Below 85% in affected herds | Above 92% with PI removal | Industry specific targets |
| Average daily gain | Reduced by 10–20% in growing cattle | Restored toward breed potential | Based on genetics and nutrition |
| Veterinary treatment costs | Higher due to repeat interventions | Lower with proactive monitoring | Tracked per animal and per hectare |
| BVD prevalence in bulk milk | Detectable antigen or antibodies at significant levels | Undetectable or consistently negative | Herd specific thresholds |
| PI animal prevalence | 1–5% in endemic situations | Near zero after eradication | Ongoing surveillance recommended |
Key Recommendations For Sustainable Control
- Screen the herd to identify and remove persistently infected animals quickly.
- Implement a structured vaccination programme tailored to breeding stock and local risks.
- Apply strict biosecurity measures for new livestock, visitors, and equipment.
- Monitor performance indicators such as calving rate and growth against benchmarks.
- Review and update the control plan with professional advice at least annually.
FAQ
Reader questions
What are the early signs that my herd may have BVD virus diarrhoea problems?
Persistent diarrhoea in youngstock, occasional abortions, repeated pyometra, and unexplained poor growth can signal BVD activity. Blood testing for antigen or antibodies helps confirm whether BVD is driving these issues.
How reliable are bulk milk antibody tests for monitoring BVD status?
Bulk milk testing is a practical herd-level tool, but it reflects cumulative exposure rather than current infection in every animal. It should be combined with targeted blood sampling of youngstock and, if available, ear notch testing to identify PI calves.
Can vaccination alone eliminate BVD virus diarrhoea from my herd?
Vaccination reduces clinical disease and viral shedding but will not clear existing persistent infections. Removing PI animals and maintaining strict biosecurity are essential alongside vaccination to interrupt sustained transmission.
What is the most cost effective approach to control BVD virus diarrhoea in medium sized dairy herds?
A phased plan that starts with blood screening to identify PI animals, followed by their prompt removal, strategic vaccination of breeding stock, and clear biosecurity protocols delivers the best long term return on investment.