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Testing calves as part of BVD monitoring and control plan will pay dividends

Tag and testing calves as part of a BVD monitoring and control plan will pay dividends when it comes to calf health and performance.

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Anyone who rears youngstock will benefit from eradicating BVD and that means embracing farm tag and testing of calves, says vet Dave Gilbert, of Horizon Dairy Vets.

 

He says: “BVD is most commonly associated with fertility reduction, but the youngstock losses are far greater if you think of the impact on immunosuppression and the myriad of diseases it can predispose youngstock to.

 

It could be impacting on your pneumonia levels.”

 

Vaccinating against BVD will provide some protection, but will not stop a persistently infected (PI) BVD animal (see panel, above), from shedding disease. These PIs are the main source of BVD spread.

 


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Persistently Infected animal (PI)

  • A PI is formed when a naive cow becomes infected with BVD virus at one to four months of pregnancy.
  • The calf is unable to mount an immune response and is born persistently infected
  • These animals will always shed disease and are the main source of BVD spread
  • A PI heifer/cow will always produce a PI calf
  • If an animal tests negative for BVD virus, you know its dam is also negative
  • Culling PIs form a key part of BVD control Tips on BVD control
  • Vaccination should be used alongside identifying and culling PIs
  • Adhering to the vaccine’s data sheet is vital – failure to store vaccines appropriately or give them at the right time could mean they do not work
  • Think about good biosecurity – buy from BVD free herds and avoid nose-to-nose contact with neighbours Tag and test
  • Caisley BVD eartags double as standard ministry approved eartags, allowing a tissue sample to be taken as part of the tagging process
  • The tissue sample is sent to CIS which handles the analysis and sends the results back to the farmer
  • A pair of ministry approved tags with a BVD tissue test costs as little as £4.30 with Caisley

Pneumonia

 

When a farm has a PI among its heifers this will lead to more pneumonia, reduced growth rates and poor production and survival.

 

“Identifying these PIs early to prevent them spreading BVD is key,” says Mr Gilbert.

 

He believes the first step in the fight against BVD is establishing a farm’s disease status.

 

Often farmers may have been vaccinating for years, but have no idea of their actual BVD status.

 

This is where blood testing and tag and testing can come in.

 

Tag and testing uses a specialist eartag to take a tissue sample from the ear as part of routine tagging.

 

This sample is then sent for analysis for BVD virus (see BVD: Did you know panel, p18). A positive reading shows the animal is likely to be a PI.

 

“The big thing about tag and testing is it makes it much easier for the farmer to execute [compared to blood testing],” adds Mr Gilbert.

 

 

Recently discovered BVD: Andy Latham, Park Farm, Cholmondeley, Cheshire

Tag and testing has enabled Andy Latham to very quickly identify and cull BVD offenders and provide him with the confidence that any stock he sells is disease free.

At the end of last year, Mr Latham was persuaded to sign up to the Stamp It Out BVD scheme by vet Laura Donovan, of Nantwich Farm Vets.

The scheme provided funding to antibody test 10 unvaccinated heifers aged nine-18 months.

Of the animals tested, 100% came back as positive for BVD antibodies, suggesting they had been exposed to the disease.

Having vaccinated against BVD for three years, Mr Latham was surprised by the results.

He says: “I was quite surprised to find that.

We now run a closed herd, but have bought two bulls in the past.” Dispersal Mr Latham was keen to get on top of the issue rapidly, considering the fact he is slowly dispersing the 150- cow Montbeliarde cross Holstein and Montbeliarde cross Brown Swiss herd, before moving into contract heifer rearing.

“I’m selling up and I want to go to auction and say we’ve done the tests, there’s no PIs and people can buy with a little more confidence,” he says.

He was consequently quick off the mark, undertaking bulk milk testing and tag and testing animals not putting milk in the tank.

The tag and test results found three PIs; one in-calf heifer and two bulling heifers – all of which Mr Latham identified as ‘poor doers’.

They were immediately culled.

Subsequently, all calves have been tag and tested and no more positive animals have been found.

Vaccination has continued.

He views tag and testing as ‘cheap insurance’ and something he would have done, regardless of the herd dispersal.

Moving forward he would like any heifers reared on contract to be BVD tested too.

“I’d like them to come here tested at 10 weeks.

BVD wants to be eradicated and the younger the animal is when we find it as a PI, the better,” he adds.

A potential monitoring strategy includes:

 

1 - Know your status

First off, a cohort of about six heifers aged more than eight months should be blood tested by the vet to assess for BVD antibodies.

 

This will tell you if they have come into contact with BVD. These animals are sentinels for the virus.

 

If they test positive, the virus could be being shed by any animal on-farm or the animal responsible may no longer be on-farm.

 

2 - If your cohort test is positive

You know that heifers have been in contact with the virus. The next step is to identify any PIs within the herd. You can either:

  • Tag and test every calf born over a two year period and cull any positive animals or
  • Immediately go back to your heifers and either tag and test or get the vet to carry out blood testing to identify and cull PIs immediately. The decision will be based on a farm’s objectives and cost.

 

3 - If your cohort test is negative

Animals are naive to BVD. It is worthwhile tag and testing all calves born on farm for two-three years so you are as confident as you can be there are no PIs on-farm.

 

After this time, you can then move to six or 12 monthly screening of youngstock to check that BVD has not re-entered.

 

Considering the huge potential cost of BVD, in terms of reduced health and performance and potential mortality, Mr Gilbert believes spending a little more on a tag, so it includes a test for BVD, is ‘smart decision-making’.

Down the line: Alan Bewster, Wester Borland, Thornhill, Stirling, Scotland

Tag and testing has formed the foundation of BVD monitoring and control at Wester Borland, where the 11,000-litre, 260-cow Holstein herd has been declared BVD negative.

Alan Bewster, wife Sophie and father William set up the herd in 2015 after moving out of suckler beef.

Having used tag and testing on the beef unit to stay on top of BVD – even before BVD eradication became compulsory in Scotland – Mr Bewster recognised the need to do the same in the dairy.

The fact the herd was established by buying-in 120 in-calf heifers from Holland, as well as fresh cows from market and private sale, also added to the risk of buying-in the problem and underlined the need to monitor.

The in-calf heifers in particular posed a risk, considering a dam can test negative for the disease, but its unborn calf can be a PI.

Every calf born both alive and dead has subsequently been tested for BVD virus with CIS, although no animal has ever tested positive.

Calf BVD status Mr Bewster is keen to establish calf BVD status early considering two-thirds of the herd is put to beef with calves sold to a rearer at about three weeks old.

He says tag and testing using Caisley tags allows calves to be tested ‘quicker and also easier’ compared to blood testing which requires calves to be batched up over 28 days before testing.

He says: “Other than gathering the vial and sending it away, tag and testing is a lot easier rather than grouping calves up for blood tests and paying the vet £1 a minute plus call out.” Test results are made available through CIS.

To date, the testing has never picked up a PI and the herd is now declared BVD negative.

“A lot that buy our calves have accredited beef herds so it keeps things right for them,” Mr Brewster adds.

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