Bovine Viral Diarrhea Virus (BVDV) or Pestivirus, is a virus that has the potential to cause significant reproductive and calf losses in unexposed herds.
Cattle that have never been exposed to BVDV and therefore have no protective antibodies are called “naïve”. After their first exposure to, and infection with BVDV, cattle develop a strong and long-lasting immunity. While infection for the first time may cause fever, diarrhoea, depression and oral ulcers, if these signs occur they are usually so mild that they go unnoticed.
Another consequence of exposure is immune suppression. In our pasture-based system, this rarely causes major problems in adult animals. Calves, however, with naturally lower immunity and high exposure to pathogens, can occasionally show signs of common diseases that are more severe or affect a greater proportion of the mob.
However, if naïve cattle are infected with BVDV for the first time when they are pregnant during the first or second trimester it is likely that there will be significant consequences for the developing foetus.
Infection around the time of conception or implantation results in reduced conception rates and increased embryonic death. Infection during the second trimester of pregnancy can lead to congenital defects as BVDV can cross the placenta and affect the foetus. These calves can be aborted, stillborn or born alive. The congenital defects include:
- Joints fixed in flexion or extension: cows often need assistance to deliver them.
- Blindness, small eyes, or no eyes.
- Lack of hair.
- Cerebellar deformity. The cerebellum controls fine motor movements and affected calves that are born alive have tremor, incoordination and stand with their legs out wide.
If the cow is infected between days 40–120 gestation the virus stays within the calf which, if born alive, will shed BVDV for the rest of its life. They are known as persistently infected animals (or “PIs”) and expose other animals to the disease.
- These PIs are the major source of infection for other animals.
- Persistently infected calves are often in poor health and die early.
- They tend to succumb to disease exposure that a healthy animal would resist.
- Some animals can make it to adulthood. For example, we have identified bulls during bull testing (when they are about to enter the herd) as being persistently infected.
- Persistently infected animals are diagnosed through ear notch testing, where we look for the presence of the virus.
Most farms in our district have some level of exposure but within any herd there may be groups of naïve animals and if they are exposed to BVDV it can be a big problem.
BVDV status can be assessed on farm by looking for:
- The presence of antibodies to the virus: either in the blood of individual animals, or in the herd’s bulk milk.
- The presence of the virus: either in the blood or tissue of individual animals, or in the herd’s bulk milk.
Management options for BVDV vary for each farm. The first step is to define your farm’s status followed by devising a farm-specific management plan:
- You can vaccinate to protect naïve animals
- Good biosecurity to prevent persistently infected animals entering farm. This could involve testing new animals (for example bulls) as they arrive on farm.
If you have any questions about BVDV please talk with one of our veterinarians.