To control BVD you must identify each animal's status and:
¦remove any persistently infected animals on-farm.
¦prevent any new persistently infected animals being born on or introduced to the farm.
¦ensure incoming PI-clear animals are not transiently infected.
PI animals are formed when naive (not immune to BVD) cows become infected with BVD in the first four to five months of pregnancy, producing a calf infected with BVD for life. PI calves often have poor immunity and appear ill-thrifty (growing more slowly than expected) but some appear normal and enter the herd. Transiently infected animals are those which are temporarily infected with BVD.
Four-step control
Ensure you work with your vet through each of these steps:
• Define:
BVD diagnostic tests are highly accurate. A simple bulk milk screening test to look for antibodies against the virus is a good place to start.
• Assess
In: Cattle coming onto the farm, including their foetuses. People, equipment and vehicles coming onto the farm.
Out: Heifers and carry-over cows grazing off-farm, including heifers returning pregnant.
Contact: Avoid cattle contact across neighbouring fences.
• Act:
Take action to create a control plan, which could include these steps:
Test incoming animals (including bulls and calves born onto the property) for the virus and cull any PI animals identified.
Make sure bulls have been fully vaccinated prior to arrival.
Vaccinated animals should still be tested to confirm they're not persistently infected.
Vaccinate cows and heifers to protect them during their pregnancy, and vaccinate bulls used for mating.
Change management practices to reduce the risk of exposure, e.g. put outriggers on boundary fences.
• Monitor:
Regular monitoring is essential to detect any incursions early and minimise their impact.
Samantha Tennent is a animal and feed developer for DairyNZ
