Bovine viral diarrhoea: Herd testing shows rising cases in Waikato

Bovine Viral Diarrhoea could potentially cause significant economic losses for farmers. Photo / Michael Cunningham

The Waikato region is experiencing a surge in bovine viral diarrhoea (BVD) cases within dairy herds, according to herd improvement company CRV.

Bulk milk testing has revealed a significantly higher number of Waikato herds testing positive for the BVD virus compared to the previous season, CRV said.

The highly contagious disease could potentially cause significant economic losses for farmers, CRV national sales and marketing manager, and vet, Julia Baynes said.

While typically only two or three herds tested positive each year, this year, the number had risen into the tens within Waikato, she said.

This was particularly alarming, considering the Ministry for Primary Industries’ figures showed widespread BVD costs New Zealand farmers an estimated $150 million annually, she said.

“With dairy farmers already grappling with a challenging economic environment, the last thing they need is a BVD outbreak.

“Given that in most cases, last season’s milk tests from affected farms did not identify any BVD virus, it is likely that the virus has been introduced to herds since the last testing cycle.

“Therefore, farmers must remain vigilant, especially as bulls are brought on to the farm for mating.”

CRV said BVD could result in embryonic loss in cows, leading to increased empty rates and significant financial losses for farmers.

It could also lead to the birth of more Persistently Infected (PI) calves if not managed correctly, exacerbating the problem.

PI animals, especially heifers, were the primary carriers of BVD.

These animals were exposed to the virus during foetal development in the first two trimesters.

If they survived to birth, they harboured a persistent infection until they joined the milking herd.

PI animals did not always exhibit classic BVD signs, such as poor growth and a scruffy appearance.

Baynes said in many cases, they appeared healthy, which made it challenging to identify them based on outward appearance alone.

“The consequences of a BVD outbreak during mating season can be devastating for farms, and it’s not always the scruffy-looking calves, heifers, or cows,”

“BVD can be a silent weapon.

“It’s not until cows are cycling well and farmers start experiencing a surge in returns from aborted foetuses that they realise something is amiss.”

Farmers were strongly encouraged to follow best practices to mitigate the risk of BVD, including annual bulk milk testing, ear notching of calves, and vaccination.

Monitoring herds for early signs of the disease was crucial since early detection could prevent the virus from spreading, Baynes said.

“Ear notching for calves is an effective way to test for the presence of the virus at a young age.

“This enables farmers to identify and remove PI animals from the herd as quickly as possible and prevent further spread of the disease.”

Vaccination was another crucial tool in the fight against BVD.

It provided protection for young stock and reduced the risk of infection during the critical period when heifers were most vulnerable, and a further pre-mating shot could give six months of protection to the foetus.

Baynes said to further safeguard the herd, it was important to ensure that any bulls brought into the herd were tested for BVD and vaccinated.

“Farmers should maintain strict biosecurity measures to prevent the introduction of the virus from external sources, particularly through bulls brought on to the farm for mating.”

For more information about BVD and best prevention practices, farmers are encouraged to consult their local veterinarians.