Vet Club BVD Seminar

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Vet ClubBVD Seminar

• April 2009Waikite Valley Hall

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What is Bovine Viral Diarrhoea ?
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• BVD is a virus that is widespread in NZ with up
  to 60 - 85 of dairy herds having antibodies to
  the BVD virus.
• With 35 having high bulk tank test antibody
  results and at least 17 of herds being actively
  infected with BVD.
• BVD often remains invisible in the herd while
  causing significant reproductive losses.
• Most non pregnant adult cattle with an acute BVD
  infection will show no obvious clinical signs.

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• BVD infection is caused by contact with infected
  faeces, urine, milk,Saliva and Semen.
• As well as abortion, BVD can cause ill thrift
  /poor milk yield and immunosuppression.
• This immunosuppression can also exacerbate the
  effect of other diseases such as Neospora and
  Rotavirus.

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• Infection of a pregnant cow with no previous
  exposure to BVD during pregnancy can cause a
  number of outcomes depending on the state of
  pregnancy.
• Exposure within the first 40 days of pregnancy
  will result in early embryonic loss and a number
  of repeat breeding cows.

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• One recent study within the same herd showed
  immune cows had a conception rate of 78 versus
  22 for those infected for BVD.

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• This is supported by work under taken by Massey
  university that showed that herds with high bulk
  milk tank antibody levels had on average increase
  of six days from calving to conception, a two
  fold increase in the abortion rate, subsequently
  these herds had a much higher induction rate due
  to delayed conception.

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• Exposure between 40 -150 days gestation results
  in either foetal abortion or small calves often
  with congenital defects that are persistently
  infected with the virus.
• P.I animals tend to continually shed the virus
  and are the main source of BVD infection within
  the herd.
• Calves that are exposed to virus over 150 days
  gestation are often small and weak but dont tend
  to be persistently infected with the virus.

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• P.I animals are likely to be poor producers more
  prone to other diseases.
• Sudden death can occur in P.I animals if the
  exposed to another strain of the BVD virus. This
  disease syndrome is known as mucosal disease it
  usually affects animals between 6-18 months of
  age.

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• If P.I animals enter the milking herd they will
  shed the virus throughout the herd for the rest
  of their life. Also Calves born to these cows
  also will be persistently infected.
• Any cows in the herd that have not been exposed
  to or developed immunity to the virus are
  vulnerable to infection.
• Which can result in abortion or more
  persistently infected animals entering the herd.

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