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Bovine Viral Diarrhoea (BVD) is a viral disease which has become widespread in New Zealand. As more research is conducted, the extent of the disease’s economic impact is becoming apparent. With around 15 % of diary herds infected, it is estimated that BVD costs the dairy industry at least $ 45 million annually. Depending on your herds’ infection status, the disease could be costing you up to $ 90/cow. For example, this could represent a cost of $ 36,000 annually for a milking her of 400 cows.

The cost to the beef industry is thought to be significant, as over 60% of beef herds are known to be infected with the virus.

 

What does it do?

 

When animals become infected they suffer a transient infection which lasts up to a few weeks.

 

Effects on young stock (3-9mths of age)

 

  •  Scouring
  •  Rough coats
  • Ill thrift
  • Coughing
  • Ulcers in mouth (sometimes!!)
  • Lameness
  • Immunosuppression
  • Often confused with parasitism
  • A large number of animals are often affected however the virus doesn’t usually cause death

 

What does it do in adult cattle?

 

Few adult cattle show clinical signs of the disease. However transient immune suppression does occur which can lead to an increased chance of contracting other diseases; leading to a reduction in production and an increase in treatment costs. The effect the disease can have on the fertility of your herd is a major area of concern.

 

The virus has different effects on cows and calfs and depends on which stage of pregnancy the cow is in when she becomes infected:

 

0 – 40 days in calf – infection will cause early embryonic loss = empty (or late calving)

 

40 – 120 days in calf – infection can cause the cow to abort or the calf will be born malformed in some way

 

120-150 days in calf – infection can cause abortion, malformed foetuses or produce calves known as persistently infected or P.I animals. These animals fail to clear the infection from their system and continue to shed the virus consequently acting as a source of infection for the herd. These calves are born antibody negative and antigen or virus positive. They are often “poor-doers” and can develop a condition called mucosal disease if the BVD virus mutates. Mucosal disease kills calves in a short period of time.

 

150 days - full term– infection of the dam will lead to the calf developing an immune response; ousting the virus from their body. These animals will be born antibody positive.

 

Points to Consider:

  • PIs are the reason this disease continues
  • PI bulls are the number one cause of introduction of BVD into a herd
  • PIs cannot be cured and should be culled from the herd

 

Preventing the effects of BVD in your herd :

 

As stated above, BVD can have a major affect on your herds’ reproductive performance. The disease is difficult to control due to its complicated nature and the fact that it is easily spread. However recently there have been advances in the tests available to help control or eradicate the disease.

 

Dairy Cows:

 

  • Bulk milk antibody testing.

This gives an indication of the level of immunity in your herd and therefore the likelihood of a current infection.

 

  • Bulk milk tests.

These tests can identify viral particles in the milk; aiding in the detection of PI animals in your herd.

 

  • Blood testing.

Blood testing individual animals can help identify P.Is.

 

Beef Cows and Dry stock:

 

  • Blood testing.

A sample of animals can be blood tested to assess the level of exposure to the virus and whether or not further testing is indicated.

 

 

A vaccine is now available, which if given pre-mating, will provide protection of the foetus throughout the pregnancy. This protection can help prevent early embryonic loss, abortion, as well as the production of P.I animals. It will also act to boost the cows’ immunity, thus preventing her from suffering from the effects of a transient infection.

 

At the bare minimum it is recommended that:

 

  • All of your bulls are blood tested to preclude the possibility of using a P.I bull for mating, which would have a disastrous affect on reproduction

 

  • All bulls should also be vaccinated pre-mating to prevent the negative affects on their performance from becoming infected during the mating period.

 

  • Dairy herds - A bulk milk BVD antibody test is performed to gauge the level of immunity and possibility of infection in your herd.

 

  • Beef herds or Dry Stock - 15 blood tests collected from the mob of animals in question – ideally done 2 months pre-mating to allow for vaccination to occur. Animals tested need to be 10 months or older when blood tested to avoid any colostral antibodies from the dam affecting the result.

 

  • Care should be taken when introducing new stock into your herd. These animals should have their BVD statuses checked and a sample of the animals tested for BVD antibody levels.

 

I realise that this is a large amount of information to take in so if you have any questions regarding BVD please feel free to contact me or members of the Large Animal team at Clutha Vets.