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Vet's View: The impact of Border disease on performance

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Border disease is caused by a pestivirus related to bovine viral diarrhoea (BVD) virus, explains Mrs Batty.

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It can be the cause of poor scanning percentages or poorer lambing percentages than normal, more abortions and stillbirths, weakly lambs, ‘hairy shakers’ and increased incidence of lamb diseases, she says.

 

“It is transmitted mainly by nose to nose contact and is most commonly introduced into a flock by a bought-in infected animal. Cattle can spread BVD virus to sheep and less commonly sheep can pass Border disease to cattle.”

 

“A SAC/Moredun study in 2006 found a third of the 125 Scottish flocks tested had evidence of exposure to Border disease,” says Mrs Batty.

 

Adult and healthy lambs exposed to Border disease show only mild signs or no clinical signs at all. Serious consequences occur when sheep are exposed during pregnancy, she explains.

Clinical signs

“Clinical signs include an increase in the number of barren ewes, abortions, still births and the birth of small weakly lambs.

 

“In some cases lambs may be born with skeletal deformities, tremors and hairy fleeces, known as hairy shakers - don’t assume that all deformed and dummy lambs are due to Schmallenberg virus infection,” says Mrs Batty.

 

“If the pregnant ewe is infected before the foetus has the ability to mount an antibody response [around 85 days], the lamb will become persistently infected with virus.

 

“These lambs are often referred to as ‘PI’s’, and may appear normal at birth, be weak or have a body tremor.”

 

Mrs Batty explains the term ‘hairy shakers’ comes from the long fibres sometime seen in the lamb’s wool.

 

Many of the PI lambs die early in life, however some apparently healthy looking lambs will survive and act as a source of infection to the rest of the flock, she adds.

 

“If you suspect Border disease in your flock, the first person to speak to is your vet. They can advice you on the most appropriate method of investigation.

 

“A diagnosis of suspect Border disease can be made based on clinical examination of a number of hairy shaker lambs.

 

“Diagnosis can be confirmed by blood sampling affected lambs for Border disease virus or by submitting dead lambs to your local AHVLA or SAC consulting veterinary disease surveillance centre.”

 

But Mrs Batty warns not all flocks will present with the classical signs.

 

“Border disease can go undiagnosed as there are numerous causes of increased abortion and barren rates.

 

“A barren rate of more than 5 per cent at scanning and an abortion rate of over 2 per cent or a number of abortions over consecutive days should be investigated,” she advises.

Blood samples

“Aborted or barren ewes can be blood sampled for the Border disease antibody and virus as part of an abortion enquiry.”

 

The flock’s status can be assessed by screening around 10 hoggs or gimmers aged six to 18 months, again for the Border disease antibody, adds Mrs Batty.

 

She says: “If you have a number of separate groups which don’t mix, then ten animals from each group should be tested.

 

“If the screen shows evidence of exposure to Border disease virus, then screening to look for the source or sources of infection should be considered by virus testing individual sheep to identify the persistently infected animal.

 

“As part of the quarantine procedure consideration should be given to blood sampling replacements for Border disease virus.”

 

Border disease

  • Investigate increased barren and abortion rates
  • Do not assume all deformed and dummy lambs are due to Schmallenberg virus
  • Screen your flock for Border disease antibody to see if it has been exposed
  • Consider testing replacements for Border disease virus
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