Up to 95 per cent of Australia’s dairy herds could have been exposed to pestivirus, including those in mainland states and Tasmanian herds.
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Pestivirus causes abortion in cows, ill-thrift, pinkeye, diarrhoea and respiratory diseases, including pneumonia.
As a result of infection in early foetal life, those calves that survive become lifelong carriers of the virus.
The virus is shed by these calves in all body secretions – saliva, tears, nasal discharges, milk, urine, semen and dung.
It is very contagious, and is spread by direct contact with the carrier animal or its secretions.
The effect on the dairy business due to pestivirus includes early foetal abortions by 40-50 per cent of female cattle across the herd.
New Zealand research into heifers affected by pestivirus indicates they produced 48 per cent less milk volume, with 48 per cent less fat and 49 per cent less protein in the vat.
After recent outbreaks of pestivirus were identified in dairy herds in Gippsland and northern Victoria, Hico hosted a workshop with dairy farmers, veterinarians and industry service providers, to raise awareness of the extent of the problem.
“We’re seeing it widespread in dairy and beef herds, and we’re seeing it in northern and southern Australia,” said David Dunlop, artificial breeding and semen sales manager for Hico Australia.
Some farmers at the Gippsland workshop on August 6 detailed their experiences realising they had pestivirus in their herds for the first time.
Every farmer’s story was similar, with pestivirus occurring some months after the purchase of new cows that were in-calf. That included cows purchased from reputable herds.
The impact on their production systems occurred after calving and weaning. Some calves remained strong, others were weak in the paddock, showing symptoms of respiratory disease.
Deaths among the calves led to tests, although pestivirus was not part of the initial testing regime. Eventually, each farm received notice of positive tests for pestivirus antibodies.
Evan Campbell and Kellie Price, from Yannathan, had a closed herd until they purchased cows from a reputable breeder.
“The calves were weaned and went to the outblock in very good condition last year,” Evan said.
The heifers on this block are monitored daily.
“Two months later, on a really hot day, five heifers died,” Evan said.
“Our vet did post-mortems and we tested the water in the dams that the heifer herd had been drinking from.
“The vet found some abdominal scarring during the post-mortems, caused by bovine viral diarrhoea virus (BVDV).”
BVDV is commonly known as pestivirus.
“Histology showed pestivirus antibodies in some of the heifers,” Evan said.
He followed up with a bulk milk test which indicated pestivirus in the herd.
“So we ear notched all the calves and the milking herd and identified one cow and two calves that were PI animals,” Evan said.
“We contacted the breeder we bought the cow from and they admitted they had a history of pestivirus in their herd.”
Evan and Kellie, with advice from their vet, are now bulk testing the milk in the vat a couple of times a year.
“I’m confident in bulk milk testing,” Evan said.
“It would be good if all dairy herds were tested through a bulk milk test, to determine the extent of the problem.”
Herd fertility has also improved.
Pestivirus creates a mass immunosuppressive event in the herd. The critical effect is caused by an animal that is called a persistently infected (PI) animal.
Australian research has indicated within a herd or group of animals in which there has been recent virus spread, the incidence of PI cattle can range from 1-50 per cent.
Dr Rob Bonanno, of ProDairy, is a veterinarian with decades of experience working with dairy herds.
“I can count on one hand the number of herds we’ve tested that haven’t been genuinely exposed to pestivirus,” he said.
“In the past 12 months, we’ve done more than 100 bulk milk tests in Victoria and Tasmania.
“We’ve found exposure everywhere we’ve looked.
“Results have ranged from really high exposure with PIs in the herd, to low sporadic exposure with no PIs present.
“It’s a widely spread disease that hides in plain sight.
“I’ve known farmers who’ve bought extremely good looking, well-bred animals, that have been PIs.
“The few herds that have managed to avoid exposure – exposure at the wrong time on that farm could result in a catastrophic outbreak of embryonic loss, PI-born calves, every calf in the calf shed infected with salmonella, pinkeye, pneumonia or other respiratory bugs.”
Rob said he had seen positive test results in calves and in four-year-old milking cows, disputing the widely held belief among farmers that PI cattle are scrawny, under-developed and die within days of being born.
He said the animal that gets pestivirus in the womb will shed millions of pathogens in its lifetime. Other cattle contract pestivirus simply by being in the same space as a PI.
“Outblocks are a disaster for pestivirus,” Rob said.
“You often don’t know if cattle or a bull from next door get in with your heifers, and one of them could be a PI.
“The farmer next door might have bought PI cattle and put them in the paddock next to your in-calf heifers, and the first time you know you have a problem is when your calving rate is low.
“Wild deer are also a carrier of pestivirus.”
Rob said in-vitro infection is the biggest risk for production loss.
“If a heifer or cow gets the disease when they’re 0-40 days pregnant, the embryo is lost,” he said.
“If you’re doing a short eight week joining, that animal is six weeks in-calf and then loses that calf, so it’s a very low likelihood of her having a successful joining again.
“So you have a heap of cows that present as empties at the end of the joining period.
“And you think, she only had one mating, we didn’t see her again, she missed joining this season.”
Between five to 15 per cent of pregnancies are lost in the embryonic stage in an given year.
But the immunosuppressive flow-on status effect of pestivirus accelerates this risk, as it does with infections.
“But if a cow is between 40 and 125 days pregnancy, if it gets infected with pestivirus, that little foetus doesn’t have an immune system. And this is where the virus is cool,” Rob said.
“The calf’s immune system never recognises pestivirus as something that doesn’t belong to it.
“So these calves never create an immune response to pestivirus and they are what we call PIs.
“And PIs spread pestivirus. For as long as they live, PIs will shed pestivirus, because their immune system recognises that as normal.
“So those PIs infect all the calves in the shed.
“When they are running with the heifer mob, those PIs infect all the heifers.
“If they get across the fence into the neighbours place, they’ll infect the neighbour’s cattle.”
If that herd shares a fenceline with other cattle, the infection will spread between animals.
Eradication of the virus within Australia’s dairy herds still puts them at risk, because the nation’s beef herds also carry PIs.
But eradication programs overseas have significantly reduced the impact of pestivirus.
A testing and eradication program in Swiss herds, including culling PIs, saw the prevalence of newborn calves born with pestivirus infection reduce to under 0.2 per cent.
Recent research in Ireland concluded the annual benefits of eradication of pestivirus from dairy herds benefited production by a factor of 14.
A six year eradication program was estimated to cost 40 per cent less than the annual production loss across the Irish dairy industry.
Meat and Livestock Australia has identified pestivirus as the second highest economic impact disease affecting cattle – with an annual estimated cost of $114.5 million.
The MLA report recommends prevention by culling PI animals and herd vaccination.
In Australia, Zoetis produces the only available vaccine for cattle, called Pestigard.
At Beef 24, Zoetis launched an online calculator for beef and dairy farmers to identify the loss of production in their herd if it is affected by pestivirus, compared to the cost of annual vaccinations.
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