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Managing pestivirus

19 Apr, 2013 04:00 AM
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BELIEVED to be endemic to about 70 per cent of Australian cattle operations, pestivirus, also known as Bovine Viral Diarrhoea Virus (BVDV), is one of the most common herd diseases in the country.

Despite its prevalence, it's a disease West Australian veterinarian Dr Enoch Bergman, Esperance, said could be eradicated with good herd management practices.

During a recent workshop held at Guyra Angus stud Bald Blair, Dr Bergman told New England producers a systematic approach was needed to wipe out the disease, which is estimated to cost affected operations $20 to $100 per breeder each year through decreased fertility rates and lower weaning weights.

The disease is spread when cattle come into contact with carriers, known as "persistently infected" (PI) animals.

While symptoms are usually mild and animals quickly develop immunity to BVDV after coming in contact with a PI animal, their immunity can be impaired and greater risk comes when pregnant cows are infected.

If infected during early pregnancy, the resulting calf will likely be born PI and will infect other animals during its life.

Dr Bergman, who set up Australia's first commercial laboratory to test for BVDV from non-blood samples, said the key to eradicating pestivirus was to "break the cycle".

"We need to make sure when the females go to the bulls they are both immune and PI free," Dr Bergman said.

He said the first step was to screen each individual mob on the property for BVDV antibodies.

"If you find a group that doesn't have an immunity, that's when you reach for (pestivirus vaccine) Pestigard," he said.

Once a producer has worked out the status of their older individual cow mobs, it is particularly important to focus on each new crop of replacement heifers BVDV status.

"When they have lived together for at least two months and are at least eight months old, blood test about five per cent of your replacement heifers for evidence of antibodies to BVDV," he said.

"If you find they're all negative, that means they haven't come into contact with a PI animal."

If the heifers are found to be highly immune, each replacement heifer should be ear notch tested to identify any persistently infected animals so they can be sold straight to slaughter and kept out of breeding mobs.

Being highly immune, they will not benefit from vaccination.

By ensuring all breeding mobs are highly immune and PI free, pestivirus could be eradicated from farms.

By continuing to blood test groups of replacement heifers, producers can monitor the success of their BVDV program and monitor for reintroduction.

Dr Bergman said shows could threaten the pestivirus-free status of herds.

He recommended quarantining show animals for 30 days after the event and vaccinating animals before sending them to the show.

"It's the same as if you send your kids away to camp, then they come back home with the flu," he said.

"Giving them 30 days to chill out before sending them back to school will protect the rest of their class.

"Many shows now require animals to be pestivirus free, reducing the risk of infection for other show animals."

However, producers should exhibit extra caution when sending pregnant animals to shows.

The progeny should be tested after birth to ensure the calf is not PI.

Dr Bergman said his method was focused on providing a cost effective way to manage the disease.

"If you blanket vaccinate everything, you're going to be vaccinating immune animals, which doesn't give you a return on your investment," he said.

Vaccinating all stock, regardless of pestivirus status, will not eradicate the disease.

"While Pestigard is a very good vaccine, no BVDV vaccine is 100 per cent efficacious," Dr Bergman said.

"If you use a non-systematic approach (such as blanket vaccination), you'll still get the occasional PI."

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READER COMMENTS

holisticmick
19/04/2013 9:58:54 AM, on The Land

If you have it. Easy fixed, run a few older cows with your maiden heifer, they are exposed and this stops it being a problem when they are pregnant. I never had a problem after that.
Cattleman
25/04/2013 12:07:24 PM, on The Land

I totally agree with this comment

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