1. Epidemiology

What is BVD?

2. Transmission

How can BVD get into my herd?

3. Impacts

How does BVD impact herd health?

4. Diagnostics

How do I know if my herd has BVD?

5. Control

How do I control BVD in my herd?

6. Eradication

How can national eradication help?

5. Control

 

If your herd is infected with BVD, the good news is that we have the tools to effectively clear the virus within 2 years.   The primary focus is on getting and keeping PI animals out of the herd since they are the main reservoir of BVD for susceptible cattle.  This is done by (1) testing all individual animals in the herd to identify and eliminate existing PIs, (2) strategically using vaccination to prevent new PIs from being created, and (3) improving herd biosecurity to stop BVD from being re-introduced after the herd is cleared.

1. Testing and Culling

This component is focused on getting rid of any existing PI animals in the herd and involves two stages. 

  • Year 1:  All animals in the herd (including calves, replacement heifers, cows, and bulls) should be individually tested for BVD virus to find any PIs.  For dairy herds, a good option is to perform a bulk milk virus test to quickly and cheaply determine if there are any PIs in the milking mob. You will still need to test all other individual animals.  For both dairy herds and beef herds, this testing can be conducted when the animals are already being yarded for other purposes such as weaning, pregnancy scanning, and routine vaccination.  Any identified PIs should be culled immediately to prevent further BVD transmission.  Any animal that tests negative for BVD virus can be certified for life as not being PI. 
     
  • Year 2: All calves born into the herd the following year should be tested for BVD virus in case there were Trojan dams carrying a PI calf when herd testing was performed or in case there was still virus circulating afterwards from transiently infected (TI) cattle.  Ideally, this should be done shortly after birth so that PI animals can be removed before other susceptible cattle can be exposed. There is no need to re-test any of the animals that were tested in Year 1. If you are not taking measures to prevent BVD re-introduction, you may need to continue testing calves each year to remove any new PIs that have been created.

2. Vaccination

Vaccination has the greatest potential benefit for (1) any herds that cannot prevent BVD from being re-introduced over time through contact with infected cattle or equipment from other farms and (2) extensive beef herds that cannot test and remove PI calves before the planned start of mating.  Although the currently available BVD vaccines can’t completely stop animals from becoming infected with BVD, they will significantly reduce the severity of clinical signs and stop the virus from crossing the placenta to harm the foetus, which will effectively reduce or eliminate the development of PI calves, weak calves, and calves with birth defects. Annual surveillance testing of newborn calves would still be recommended to identify any “breakthrough” PI calves which may have been born in spite of vaccination.

There are currently two commercial BVD vaccines available in New Zealand:

Bovilis BVD

 

Ultravac BVD

 

This is an inactivated vaccine that can be given to provide up to 12 months of foetal protection and 12 months duration of immunity to the animal.

Animals that have not been vaccinated previously should receive two shots. These can be given anywhere from 4 weeks to 6 months apart.  The booster dose should be given 2 to 4 weeks before the planned start of mating.

Animals that have been vaccinated previously should receive one annual shot ideally given 3 to 4 weeks prior to mating.

 

This is an inactivated vaccine that can be given to provide 6 months of foetal protection and 12 months duration of immunity to the animal.

Animals that have not been vaccinated previously should receive two shots.  These can be given anywhere from 4 weeks to 6 months apart.  The booster dose should be given 2 to 4 weeks before the planned start of mating.

Animals that have been vaccinated previously should receive one annual shot ideally given 2 to 4 weeks prior to mating.

Bovilis ® BVD Product Label

 

Ultravac ® BVD Product Label

Any female cattle that will be used for breeding in the current season (including mature cows and replacement heifers) should be vaccinated.  Since the duration of foetal protection only lasts 6 months, you give the vaccines at the recommended times to ensure that foetal protection will last through the time period when the herd is at risk for generating PI calves.  Remember that replacement heifers and any cows that have not been vaccinated before will need a first booster at the appropriate time before that.  It is also important to vaccinate bulls since they can shed virus in their semen for up to 2 weeks if they become transiently infected.  This can be a major source of transmission to cows during the breeding season.  BVD can also decrease semen quality for up to 8 weeks, which can impact reproductive performance for the season.  Calves can be vaccinated to prevent diarrhoea and ill-thrift associated with acute BVD infection.   Although you can also choose to vaccinate calves and other youngstock that will not be used for breeding, it is probably not a cost-effective for most cattle herds since the main economic losses from BVD are due to poor reproductive performance.

3. Improving Biosecurity

Once your herd has cleared BVD, it is important to prevent disease re-introductions from other outside sources. This will include:

  • Vaccinating heifers and dams that will be grazed or moved off-site during any stage of pregnancy
  • Testing all purchased stock for BVD virus prior to moving them onto farm
  • Maintaining good fenceline boundaries between your cattle and neighbouring stock to prevent nose-to-nose contact
  • Cleaning and disinfecting all clothing, vehicles, and equipment that have been in contact with other cattle

If you cannot effectively prevent BVD from crossing your farm boundary, then you may also have to consider long-term vaccination of all breeding dams and bulls prior to mating.  All of these preventative measures do come with a cost, which is one of the big reasons why we are pushing for national BVD eradication so that there is no longer a risk of re-introduction once your herd has been cleared.

Why "Natural Vaccination" Won't Work

Vaccination can be expensive and farmers with BVD in their herds often ask about leaving PI animals to act as “natural vaccinators” (i.e. causing transient infections in susceptible cattle so that they develop a natural and lifelong immunity to BVD). This is a bad idea for several reasons:

     1.   In many herds, especially extensive beef herds, there may not be enough contact between animals to ensure that all susceptible breeding animals are exposed to BVD prior to the breeding season.  This puts animals at risk of getting infected with BVD during the mating period when they are at greatest risk of having reproductive complications.

     2.  Animals that become transiently infected with BVD still experience decreased milk yields, slower growth rates, and increased susceptibility to other   costly infectious diseases.  These costs alone may be enough to offset the expense of vaccination.

     3.  As long as your herd has PI animals, you are at risk of infecting other herds that purchase your cattle, share grazing pastures, have nose-to-nose contact over fences, or come in contact with contaminated vehicles, clothing, and equipment.