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Sheep special: Serious implications of an MV breakdown
Bought-in stock is the most common way that a new disease is introduced into a flock and in the case of maedi visna (MV) the consequences can be far reaching.
Angela Calvert
For MV accredited flocks, a breakdown has obvious health implications, but also the financial impact of not being able to sell stock can be huge.
Lynn Gibson, SAC Consulting Veterinary Services and Premium Sheep and Goat Health Scheme (PSGHS) veterinary manager says: “The risk of a breakdown is low in MV accredited flocks and on average only 0.2 per cent of accredited flocks will lose their status due to infection each year.
“When infection is found, it is usually at a low level because members undertake regular monitoring – but the consequences both financially and emotionally can be significant.”
She explains that when infection is found, every effort is made to establish where it has originated from and if there is potential for it to have spread to other MV accredited flocks.
“Where a positive animal has been purchased, the flock of origin is tested. All animals sold from the infected flocks to other MV accredited flocks are traced and tested. This requires co-operation from the flock owners, breed societies, marts and show organisers.
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“The cause of a recent MV outbreak was investigated and contact with the farm’s non-accredited flock (which was found to be infected with MV) was suspected to be the cause.
“This biosecurity breakdown had far-reaching implications; 77 flocks had to perform tracing tests and two flocks were found to be infected.
Common factors associated with breakdowns include adding accredited animals to the flock as well as contact with non-MV accredited animals on the same holding.
Ms Gibson says: “The domino effect can be significant as one biosecurity breach in a flock can have far-reaching consequences.”
As a result, the PSGHS rules are being tightened. In accredited UK flocks it is recommended that animals are tested at the point of purchase and it is a requirement that they are tested between six and 12 months after they enter the flock and this rule will be rigorously enforced.
Non-accredited animals must be isolated and undergo two tests six months apart before they enter an accredited flock.
MV symptoms
- Weight loss, pneumonia, mastitis, arthritis and hind limb paralysis.
- MV is difficult to diagnose due to its long incubation period and clinical signs are often not seen until at least 50 per cent of the sheep in a flock are infected.
- The disease is fatal, with no current cure or vaccine available.
- For more information visit: www.sheepandgoathealth.co.uk
Take steps to avoid an MV breakdown
- Embryo transfer recipients must be accredited.
- MV is transmitted by nose-to-nose contact and aerosol spread. It can also pass on in infected equipment.
- Transportation should not be shared with non-accredited animals and if possible dedicated ‘tup taxis’ carrying only MV accredited animals should be use to transport animals to lorries/trailers.
- Check the certification of any flock purchased from to ensure that they are MV accredited.
- Imports: The flock owners must isolate the animals and provide the PSGHS office certification from the country of origin proving they are accredited along with an import declaration (certification is not required for NI and Ireland)
Commercial flock prevalence
A prevalence survey in 2010 in the national flock found that in the previous 15-year period the number of flocks with MV doubled from 1.4 per cent to 2.8 per cent.
The number of infected sheep increased from 2 per 1,000 to 8 per 1,000.
Within affected flocks the average proportion of infected sheep increased from 13 per cent to 24 per cent.
There appears to be a growing awareness of the disease among commercial flocks and Scotland’s Rural College report an increase in the uptake of their MV diagnostic test, which blood tests a sample of 12 ewes in the flock. This has risen from 35 flocks using the screening in 2015 to 110 in 2017.
MV infection can cost £30/ewe in commercial flocks (higher in pedigree flocks) in lost production but thousands if the infection leads to a complete restock. It can cost MV members significant sums in lost sales revenue, reputation and genetic loss, as well as the emotional upset losing flock health status causes.
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