Bovine Viral Diarrhoea (BVD)

BVD infection in adult dairy cows can cause reproductive wastage, weight loss and reduced milk yield. BVD also causes immune suppression, meaning cattle that have an active infection will be more likely to succumb to other diseases.
Overview
• BVD is caused by Bovine Viral Diarrhoea (BVD) Virus
• Can affect animals of all ages, but is most significant in pregnant animals
• Virus is spread via infected body fluids including semen and uterine secretions
• Virus can survive in the environment for up to 7 days and can be spread across fence lines
• Incidence of BVD in NZ:
60% of cattle have been exposed
80% of herds have been exposed
15% of dairy herds have active infection at any one time (beef herds may be much higher)
• Cost of disease is estimated at > $220 per cow in an infected herd (www.controlbvd.org.nz)
• Loss due to Transient Infection (see below):
$81 per newly infected cow
• Loss due to Persistent Infection (see below): $35/cow in actively infected herd BVD Infection
Two main types of infection:
1. Transient Infection (TI)
• Tempory infection occurring in any age animal
• High morbidity, low mortality (many get ill, few die)
• Clinical signs include (not all present at same time):
- Production loss
- Reduced daily weight gain & ill thrift
- Immune suppression leading to increased clinical disease such as mastitis, pneumonia etc
- Coughing and pneumonia in young stock
- Rough coats
- Ulcers in mouth
- Lameness
- May be confused with parasitism
2. Persistent Infection (carrier status)
• If a cow comes in contact with BVD virus while pregnant, she may give birth to a persistently infected (PI) calf. This calf will shed the virus its entire life causing transient infections in other animals. PI’s are the biggest source of BVD virus in a herd.
• Mucosal Disease
- PI which is super infected with a different strain of BVD virus, 100%fatal usually within a few days.
- Clinical signs: Diarrhoea, ulcers along the digestive tract, ulcers on feet & nose, severe weight loss.
Effects of BVD on fertility
• Cow fertility- BVD can cause the following:
- Abortions
- Early embryonic deaths (long returns)
- PI calves
- Developmental defects
- Mummified foetus
- Still borns
- Immunosuppression leading to other causes of abortions, e.g. neospora, fungal
• Bull fertility
- PI animals will spread virus through herd
- TI animals will shed virus in semen for up to 2 weeks, their semen will be of decreased quality for up to 8 weeks.
When should I consider that BVD might be causing a problem in my herd?
• High empty rate
• Long returns (intervals of 24 – 42 days)
• A high % of cows calving as ‘late calvers’
• Weaner ill thrift
• Abortions
• Mummified foetuses
• Deformed calves
• Calf losses
• Yearling deaths
Control
• There have been several improvements made in testing/control of BVD
• As a minimum all bulls should be tested and vaccinated. This is good risk assurance as it will decrease risk of bulls bringing in the disease to your herd and/or getting infected from your herd
• A practical approach to BVD control on your farm can be discussed with your vet. There are many ways to tackle this very complex disease. This will vary from farm to farm and is best discussed on a case-by-case basis.
For further information please talk to your vet.


Date Added: Tuesday, 30th June 2015


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