Biosecurity with Samantha Tennent: Don't let costly disease run away on you

Managing bovine viral diarrhoea (BVD) should be an important part of farmers' biosecurity measures.

Failing to do so can be costly: studies in New Zealand put the cost at between about $110 and $180 per cow, or about $70,000 annually for an average-sized infected herd.
About BVD

Sub-fertility, abortions, reduced milk production and calf diarrhoea and pneumonia are common symptoms of BVD virus infection.

However, the symptoms of BVD can look similar to other diseases, so testing is essential to confirm its presence.

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.

Learn more

Get more BVD information and resources at dairynz.co.nz/bvd

Check out our biosecurity information (and the Biosecurity WOF) at dairynz.co.nz/biosecurity

• Samantha Tennent is a animal and feed developer for DairyNZ