November 4, 2012

Maedi Visna

Maedi Visna Accreditation Scheme

We would urge all new flocks to join the Maedi Visna Accreditation Scheme. If you have recently purchased stock then you should contact the Sheep & Goat Health Scheme, Greycrook, St Boswells  TD6 0EQ, Telephone 01835 822456 for full details of the scheme.

SAC vets are urging sheep farmers who sell breeding sheep to join the Maedi Visna (MV) Accreditation Scheme, as the disease becomes more common in non-accredited flocks.

SAC Veterinary Investigation Officer Catriona Ritchie said: “Some farmers may think because MV is not widely recognised, that it is not worth joining the scheme but the incidence of MV is increasing.”

“So our message to sheep farmers is that you can buy from an MV-accredited flock confident in the knowledge you’re not buying in the disease. In the unlikely event that there is a breakdown, early testing provides the best opportunity for eradication. By joining the scheme, your flock will benefit from regular testing.”

“MV can cause severe economic losses in infected sheep flocks through deaths from pneumonia and wasting and its knock-on effects such as poorer fertility, reduced milk production resulting in increased lamb losses and lower weight gains in lambs. There are also losses from the premature culling of adult sheep because of mastitis, occasionally arthritis and paralysis.

If your flock is not part of the scheme then you may like to consider joining.

Contact Sheep & Goat Health Scheme, tel : 01835 822456.

If you want to check which flocks are in the scheme then consult their website

Survey Finds MV Infection Levels Doubled in 15 years – Sheep Disease July, 2012.

The number of flocks infected with Maedi Visna (MV) virus has doubled in a 15 year period, increasing from 1.4% to 2.8%, a survey undertaken by SAC and Animal Health and Veterinary Laboratories Agency has found. The survey is the first to look at the level of MV infection in the GB flock since 1995.

Funded by EBLEX and HCC (Meat Promotion Wales) the survey also found that the number of infected sheep has increased four-fold, while the level of infection within infected flocks has increased from 13% to 24%. In addition to the evidence showing an increase in MV, the number of flocks suffering significant economic effects due to high levels of infection has also risen in recent years. However the number of cases diagnosed is currently low, compared with other common sheep diseases.

There is no cure for MV and no vaccine to prevent or control it. Infection spreads through close contact, so intensively-managed flocks tend to have more infected sheep. By the time that signs of infection are seen, usually years after the virus has been introduced, it has reached such a high level it is very difficult to control.

Visible signs of MV are not usually seen until about half of the adult flock is infected. The key signs are loss of body condition, poorer fertility, mastitis, increased twin lamb disease, smaller and weaker lambs born, leading to increased mortality. A lower volume of and poorer quality colostrum and milk can lead  to reduced lamb growth rates. Fortunately MV is not a disease that affects humans.

In heavily infected flocks an increased number of deaths in adult sheep are usually reported, often due to a secondary Pasteurella pneumonia. For example in a 500 cross-bred ewe flock, investigated by SAC, the adult mortality rate was 6% in 2010 and 8% in 2011. In just the first four months of 2012 it has reached 5%. In this flock, in a short period of six months, sixteen ewes had developed severe arthritis or hind limb paralysis, caused by MV, and had to be culled. The losses due to this increased mortality, compared to a typical flock with 3% mortality, were calculated as £10,210.

Another large, heavily-infected flock had a ewe mortality rate of 8% and was having to cull a further 70-100 ewes each year, due to mastitis resulting from MV. The flock had been experiencing a high level of mastitis for some time but it was not discovered until a few years later that MV was the underlying problem.

According to SAC vet, Catriona Ritchie

“Sheep farmers in GB are fortunate the level of MV infection in the national flock is still at a relatively low level compared to countries like Spain, Italy, Belgium and the Netherlands, with significant numbers of infected flocks. Undoubtedly the existence over the last three decades of the MV accreditation scheme  has helped keep the infection levels in Britain’s flock at  a relatively low level, especially as many pedigree, terminal sire flocks are accredited free of infection. However flock owners should not be complacent. As this survey shows, levels of MV are rising”.

The advice to flock owners is to purchase uninfected sheep and use the MV accreditation scheme, to try and keep infection out of flocks. Producers should be aware of the signs of MV and if they are concerned that it may be present in their flock, should discuss this with their vet. The vet can take samples and, if the disease is confirmed, can advise on how best to manage the situation. In some cases culling and restocking may be the best option.

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