- 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 but can also be airborne
- 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% – 20% of dairy herds have active infection at any one time (beef herds may be much higher)
- Cost of disease is estimated at $70,000/year per infected average size herd. (www.controlbvd.org.nz). This doesn’t include the cost of immune suppression resulting in other diseases. e.g. Mastitis and effects on young stock.
Two main types of BVD 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
- May be confused with parasitism
2. Persistent Infection (PI) (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 and don’t respond to being vaccinated.
- PI which is superinfected with a different strain of BVD virus, and is 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:
- Early embryonic deaths (long returns)
- PI calves
- Developmental defects
- Mummified foetus
- Still borns
- Immunosuppression leading to other causes of abortions, e.g. neospora, fungal
- 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 3–4 months.
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
- Mummified foetuses
- Deformed calves
- Calf losses
- Yearling deaths
- There have been several improvements made in testing/control of BVD and the economics of control stack up no matter the farm system.
- As a minimum all bulls should be tested and vaccinated but the more you do to control the disease the more you save.
- 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.
- Talk to your vet and visit www.controlbvd.org.nz for more information.