Majority of UK herds are infected with BVD

21 September 2001

Majority of UK herds are infected with BVD

By Marianne Curtis

DESPITE foot-and-mouth being the virus at the forefront of minds this year, 95% of UK cattle herds are infected with bovine viral diarrhoea virus.

With cost/infected suckler cow estimated at £46 and BVD a contributing factor in many calf diseases, a control policy is worthwhile, Joe Brownlie of the Royal Vet College told producers at Beef 2001.

BVD should not be ignored. "Although it is considered a mild infection, it can disable calves immune systems making them more susceptible to diseases such as pneumonia."

Infection with the disease in early pregnancy can also spell disaster for herd fertility. "In one study of a herd infected with BVD, conception rates were reduced from 79% in immune cows to 22% in infected cattle," said Prof Brownlie.

But many producers dont realise they have the disease, claimed Wilts-based vet Keith Cutler. "The disease is spread by infected animals or persistently infected calves."

Persistently infected (PI) calves catch the disease from their dam in early pregnancy, before their immune system has had chance to develop, he said. "This means they think BVD virus is a normal part of their body and fail to mount an immune response to it, so continuing to shed virus throughout their life."

Both vets agreed that culling PI animals was necessary to achieve effective control of BVD, but one producer had received conflicting advice. "I was told the cost of testing animals and vaccination was higher than not treating them and the best policy was to ensure all heifers were exposed to a PI animal before mating," said Mr Cutler.

But retaining PI animals in herds was a risky strategy, according to Prof Brownlie. "This was the advice before reliable vaccines became available, however, studies show where no vaccine is used only 40% of heifers develop immunity to BVD naturally, meaning 60% remain susceptible. The last thing needed is a PI animal escaping and mixing with susceptible breeding animals.

"In recent years vaccines have also come down in price, making them a more affordable option."

Testing for the disease, which is necessary to eradicate it, is expensive, admitted Mr Cutler. "Two tests are available. The first checks whether cattle are immune to BVD and costs about £6/head. Cattle with no antibodies are either PI animals or have never encountered BVD and must, therefore, be tested for virus, which costs £6.40/head."

Finally, animals with virus may have it either because they are PI or because they have just contracted BVD, so must be tested again three or four weeks later. Those with virus after this time are PI and should be culled.

Keeping the disease out of a clear herd, however, remains a challenge, said Mr Cutler. "Secure boundary fencing is required to ensure animals have no contact with neighbouring stock. All replacements must be quarantined and tested for BVD before joining the rest of the herd."

Just one lapse in bio-security can put clean herds at risk, he warned. "One client introduced a foster calf from a dairy herd where he sourced replacement suckler heifers which had always tested BVD free. Unfortunately, the calf proved to be PI. Pregnancy rates fell from 90% to 72% and seven out of 87 calves born were PI." &#42


&#8226 Costs £46/cow.

&#8226 95% of herds infected.

&#8226 Cull PIs and vaccinate.

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