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BVD in cattle – testing & risk management
Cattle affected by BVD show poor reproductive performance and have unthrifty calves. So don’t take chances when it comes to BVD in cattle.
BVD introduction
Bovine Viral Diarrhoea or BVD is a viral disease affecting dairy and beef cattle in New Zealand. BVD can be associated with poor reproductive performance, and decreased growth rates in young stock leading to a potential reduction in the life-time performance of the individual animal and the herd.
The BVD virus is spread in oral, eye and nasal discharges, faeces, urine, milk and semen from infected animals. The virus does not survive for long in the environment but is stable below 10°C, even surviving deep-freezing of bull semen. It’s estimated that 80% of dairy herds in New Zealand have had exposure to BVD, and 60% of all cattle in New Zealand have been exposed.
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The course of the disease
BVD infection during pregnancy
When pregnant animals become infected with BVD for the first time, there are a few scenarios that can occur:
- abortion
- early embryonic loss (shows in increased empty rate, or delayed returns to heat)
- birth defects or mummified foetus
- stillborn calves or weak calves
- birth of a live but ‘persistently infected’ (PI) calf
BVD in bulls
PI Calves
A PI (persistently infected) calf can be born when the dam is infected during pregnancy. The BVD virus enters the calf and lives there without the calf mounting an immune response to eliminate it. These calves carry the virus for their lifetime and continually shed the virus into the environment. Thus, they are a large potential source of infection for other animals. PI animals are often ill-thrifty and poor doers, but not always. In some cases the BVD virus will change slightly and cause a fatal disease in older PI animals.
BVD in Cattle: diagnosis
Other BVD tests
Certain tests can detect the BVD virus itself in the herd's milk. It is sensitive enough to detect if there is even one PI animal shedding the virus into the milk. The PCR test is a positive or negative test.
Individual cow testing:
- Blood tests can determine both exposure and whether the animal is a PI or not; used to find and confirm PI animals.
- Individual milk samples can be tested to find and confirm a PI within a herd.
- Ear notch tests can be used to screen calves for BVD, and to check for PI status.
Abortion samples on aborted foetuses can confirm BVD as a cause of abortion.
The Impact
Management and Control
Control of BVD involves a combination of testing, monitoring, biosecurity and vaccination. BVD risk management means having a programme in place to ensure the virus is not introduced to your herd, vaccinating young stock, preventing over-the-fence animal contact and regular surveillance testing of the herd and young breeding stock.
BVD can be a frustrating, costly and complex disease, but understanding how it can affect your herd and managing the risks can limit the effect it can have on your business. Please contact your nearest VetEnt clinic to learn more about how to monitor and manage BVD on your farm.
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