The graph below is displaying results from a herd that has been BVD testing on the LIC BVD Monitoring Pack for four seasons. The herd was BVD negative season 2010/11 with low to moderate exposure.
Testing for year 2011/12 showed a positive BVD result indicating a BVD carrier (Persistently Infected animal) in the milking herd. The exposure level has increased to high.
The BVD carrier(s) have left the herd during Autumn/Winter 2012 and the herd tested PCR negative the following seasons. Note a decreasing exposure level due to no contact with BVD.
Reading your report
Very High Exposure (BVD-Infected herds)
The herd is likely to have active BVD infection (although antibody levels may remain high for some time after PI removal). About 40% of herds in this band have a milking PI cow and will be POSITIVE on the bulk milk BVD PCR. But many more herds may have non-milking PIs only e.g. bull, calves, carry-over, beefies or other dry stock.
Most of the cows in the herd have been exposed to BVD virus. Up to 10% of these herds will also have a milking PI. The milking herd may be exposed intermittently or had recent contact with a PI (e.g. in-contact herd with BVD). There may be a PI amongst the replacement heifers. Once PIs in a milking herd have been culled or died, antibodies will fall slowly (depends if heifers or herd continue to be exposed).
Roughly half the herd has had contact with BVD. The BVD or PI exposure is likely to be historical or the herd may have occasional contact with BVD virus e.g. over fence with neighbour’s herd. The heifers may have had contact with PIs at grazing. Recent introduction of infection or vaccination will result in a rising antibody titre, but active BVD will push levels to high – very high.
Historical exposure to BVD or PIs – up to a third of the cows in in the herd have some immunity. Generally older cows may be immune or specific mobs e.g. purchased cows, returned heifers. The milking herd is unlikely to have active BVD infection and should be protected against re-introduction of BVD virus. Assess risks and implement a BVD control plant with your vet.
No exposure (BVD-Free)
The herd show little sign of previous exposure to BVD or PIs and was essentially free of BVD at the time of testing. Great result – the herd has not been affected by BVD infection so this is the ideal situation. However, all or most cows are susceptible to BVD, so on going vigilance and biosecurity is paramount! Test all bulls or new stock. Consider vaccination to protect pregnant cows.
Consult your veterinarian to develop a complete program to protect your herd against BVD incursions.