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Maedi visna on increase in commercial flocks

Maedi visna (MV) infection has been found in 20 per cent of commercial flocks taking up SAC consulting diagnostic test between May 2016 and May 2017. 

The owners of six of these flocks reported seeing typical signs of MV including increased number of deaths, problems with thin ewes, breathlessness in adult sheep, and increased cases of mastitis. As signs of MV are not usually seen until about half of the animals in the flock are infected, it is likely these flocks had high levels of infection.


Affected ewes are often thin and give birth to smaller, weaker lambs that tend to have reduced growth rates and often fail to reach weaning targets. This is due to reduced milk supply from ewes. Affected sheep tend to be more susceptible to secondary infections particularly to pasteurella pneumonia.


Kath Dunn, veterinary investigation officer at SAC, says: “MV virus is transmitted through ingestion of infected colostrum or milk and via nose to nose contact and aerosol transfer.


“A single infected bought in sheep has the potential to infect an entire flock. MV has a long incubation period so clinical signs can take a number of years to develop. The first indication of a problem may include an increase in cull rates, thinner ewes and increased barren rates.


“Infected sheep never develop a protective immunity and there is no effective treatment or vaccination. Once a flock becomes heavily infected MV can have a major effect on a flock’s productivity and can have major economic consequences. Often the only economic option in a heavily infected flock is to depopulate and restock.”

What can I do if I suspect my flock is infected?

There is a cheap, simple way of identifying if MV could be causing problems in your flock. Arrange with your vet to blood sample some of the older, thinner ewes and rams to test for MV infection. Just after scanning is a good time to collect these samples.


An initial screen of 12 sheep can be tested for a package price of £38+VAT for the laboratory fees plus vet’s charges for collecting the blood samples. The results of this MV diagnostic test will show whether MV is likely to be the cause of disease and enable you to take appropriate action to stem the losses.

Key points

  • The number of flocks in the UK infected with MV virus is increasing
  • If you are suspect your flock is infected with MV – screen for it
  • An initial screen of 12 thinner sheep will tell you if MV is the likely cause of disease in your flock
  • The longer the disease circulates in your flock the harder it will be to eradicate or control it and the more impact it will have on your flock’s productivity
  • One infected bought-in animal is sufficient to infect your flock
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