BVD (bovine viral diarrhoea) is a widespread viral disease of cattle, and most beef herds in NZ have been exposed to BVD in some way.
There are two types of tests for BVD antibody – the immune response to the virus, and antigen (active virus shedding).
Antibody testing is used to determine exposure at the herd level. It can be tested by milk (impractical for our beef herds….) or from blood. Each age group of animals should have 15 animals tested unless grazed together. It produces a sample to positive control (S/P) ratio, which can be sorted into three categories:
- <0.17 – There is no evidence of exposure to BVD
- 0.17 to 0.75 – Group has had exposure, but unlikely to have a current PI within the group.
- >/= to 0.75 – Group has either an infected animal present, or has recently been exposed.
If your group of animals fits into the last range, the next step is to test for active infections; Antigen testing is used to find either transiently (TI) or persistently infected (PI) animals, and can be looked for in milk, blood or skin samples. Persistently infected animals should be culled as they spread the virus rapidly, and pass it on to their offspring.
Remember your bulls must always be tested and vaccinated for two-fold reasons, they can catch BVD transiently which will drop their fertility for 90 days plus, and if they are persistently infected, can spread BVD through a naïve herd causing reproductive and production issues.
In review, the steps for BVD control in beef herds is:
- Assess your biosecurity practices (animals in, animals grazed out, over the fence exposure)
- Define the herd exposure with a pooled serum Antibody test (15 from each category)
- If positive, find and remove persistently infected animals OR step by step eradication (test each year’s replacements, vaccinate the animals to be mated)
- Control via strict biosecurity or vaccination.
If you are concerned that you have an active infection in your herd, want to know your current status, or have any questions at all regarding BVD, give your local Anexa vet a call.