Anecdotal evidence suggests growing numbers of
producers are noticing older ewes losing condition, many
attributing this to old age. However, maedi visna is
becoming more prevalent in the national flock.
Peter Fairbank answers frequently asked questions
What is maedi visna?
Maedi visna (MV) is a chronic disease of sheep caused by a slow virus. Sheep with MV may show the following symptoms which can take up to three years to develop following infection: Pneumonia, mastitis, wasting and swollen joints.
These are symptoms of other diseases too, so MV is impossible to diagnose by clinical examination alone. It is often diagnosed with other diseases such as sheep pulmonary adenomatosis (SPA or Jaagsiekte).
How would it affect me?
Pedigree flocks would lose their MV accredited status and be unable to sell to other breeders at many breed society sales.
This has a big financial impact on businesses, together with the loss of many years of genetic selection.
In commercial flocks the disease is harder to cost. But with up to 50% of a flock infected before clinical cases are observed, losses develop over a long period and are often not attributed to the disease in its early stages.
With dead ewes, rather than culls to sell, and more replacements needed, flock replacement costs can double. Increased mastitis results in poorer lamb growth, increases lamb mortality and delays sales.
Both these problems increase labour input while reducing flock output at a time when all but top-third performing flocks are unlikely to be showing any profit.
Is the disease on the increase?
We dont know, but with 1.5% of flocks infected in a national survey in 1996, it is likely to have increased since. With the current lack of profitability in the industry, vets are not being consulted on disease problems, producers having the attitude that the first loss is the best.
Sadly DEFRA does not consider MV a high priority as it is not a zoonosis, but reports from the State Veterinary Service indicate more cases identified at post mortem and confirmed by histopathology.
It is concerned that MV is going undiagnosed in many flocks and these could be a potential infection risk for the rest.
To help the industry, the Sheep and Goat Health Scheme has introduced a confidential diagnostic test available free to the first 500 commercial flocks applying. For further details please contact the SGHS stand.
The SGHS has also been challenged by the National Sheep Association to increase awareness and highlight the potential threat from MV to the industry.
As part of the programme, we are running a competition at Sheep 2002. The first prize is a £300 voucher to be used for the purchase of an MV accredited ram. The winning entry will be drawn at 4pm by John Thorley. *
Although maedi visna can go undetected for years it can have a severe impact on returns, says Peter Fairbank.
• On increase.
• May go undetected.
• Testing available.