BVD – unseen disease that clobbers herds
By Marianne Curtis
BOVINE viral diarrhoea could be causing up to a 10% production loss in many beef herds, yet producers are likely to be unaware of its presence, warns SAC beef researcher Basil Lowman.
"BVD is a nasty disease and most suckler herds have it," he says. "Introducing it into a clear herd can have devastating effects. But in most herds it is a rumbling problem, knocking 5-10% off every aspect of production."
When BVD infects cows during pregnancy it causes reabsorption, abortion or death of calves soon after birth. Some calves survive, but these carry and excrete the virus, infecting other animals in the herd.
BVD reduces immunity, meaning infected youngstock are more susceptible to other diseases such as pneumonia and scours, and their performance is poorer. "You may have a serious pneumonia outbreak, but BVD is not a disease giving rise to a single problem," adds Dr Lowman.
"Losing three more calves than you should, having a few more barren cows than you expect or never quite achieving a 95% calving rate could point to BVD."
Production losses and mortality mean the cost of the disease can amount to £2000-£3000 in a 100-cow herd, says Dr Lowman. But so far it has been difficult for beef producers to assess the extent of the problem in their herds, says vet James Allcock of Intervet.
"In dairy herds it is relatively easy to check for BVD using bulk milk sampling, however, this is not practical for beef herds. Blood sampling is the only way to answer the question of whether the disease is a problem now, or has been in the past."
In a new initiative, Intervet is offering to pay the laboratory costs of blood sampling six animals in a beef herd. "Producers can decide to test either older or younger animals. Choosing to test both groups costs £20.
"Testing adults will give an indication of whether they have come across the disease in their lifetime, whereas youngstock tests will tell you whether it is active at the moment.
"Checking older animals gives the best indication of the herds disease status, especially when stock replacement policies have remained the same."
Mature cattle which have been exposed to the virus wont benefit from vaccination, as they will have developed immunity. However, vaccinating replacement heifers or bought-in animals will help avoid production losses, explains Mr Allcock.
"Vaccination involves two doses, the first costing £3 and the second being offered free for a limited period. Booster doses are required annually and cost a further £3/head."
Alternatively, producers mainly breeding their own replacements and operating a closed herd, well separated from their neighbours, can blood test the whole herd and enter a screening and eradication programme, says Mr Allcock.
Dr Lowman believes that if vaccination avoids only one barren cow, it is worth it. But he is concerned by the indifferent attitude to the disease in the UK.
"Most animals are infected by a carrier animal excreting the virus. This means markets are dangerous places for breeding stock because it only takes one animal to cough to infect many others in its vicinity.
"It is time markets had BVD-free areas. We are lagging behind the rest of the world in our efforts to eradicate this disease."
says Dr Lowman.
• Most herds infected.
• Production losses 10%.
• Free blood testing.