Sheep Farmers Urged to Step Up Vigilance for Maedi Visna

The need for commercial sheep farmers to make looking for signs for Maedi Visna (MV) in their flocks an absolute priority was a key message at this week’s meeting of the Borders Monitor Farm.

Vet Andrew Robinson from Hawick Vets, who was a speaker at the meeting, said his practice had seen a sharp increase in the incidence of MV in the borders over the last 12 months. He urged farmers to check whether their flocks are infected through a simple blood test.

“After a long period where we’d seen almost no cases, the practice diagnosed MV in a commercial flock in February 2017 and we have seen several other cases in the last few months.”

He added: “I think MV is seriously underdiagnosed so we have no idea how many flocks are infected in this area. We really need to know the true incidence so that we can advise farmers how to control and eradicate it. We would strongly encourage farmers to test their flocks for MV.”

Maedi Visna is a highly infectious disease of sheep and is caused by a retrovirus. It is spread mainly by nose to nose contact, but can also be spread through colostrum and milk. There is also a small risk of the virus passing through the placenta to the unborn lamb and venerally from ram to ewe. There is no vaccine or cure.

MV is often referred to as an “iceberg disease” because it can take several years before infected sheep show any clinical signs, so the number of animals showing clinical signs are merely “the tip of the iceberg” to the true number of animals that may be infected.

The clinical signs for MV are varied and include a decrease in scanning percentage, reduced milk production in ewes leading to lower growth rates in lambs, ill thrift, laboured breathing and increased risk of bacterial pneumonia infection and a higher cull rate. As the clinical signs are so varied, MV is difficult to diagnose in a flock.

Lynn Gibson, manager of the MV Accreditation Scheme and a veterinary investigation officer at SAC Consulting St Boswells, also spoke at the meeting and urged farmers to consider testing for MV in their own flocks.

She said: “Although sheep infected with MV can survive without showing any clinical signs for several years, they will be infectious and able to pass the virus onto other sheep in the flock.

“It’s therefore vital for farmers to try and establish if they have MV in their flock and determine how many animals are infected, so that they can discuss effective control options with their vet.”

One local farmer who knows first-hand the impact that MV can have on a flock is Scott Brown from Stonefieldhill Farm, a member of the Borders Monitor Farm management group. MV was diagnosed in his MV accredited pedigree Texel and Suffolk flocks in 1997. Before MV was confirmed, Mr Brown had noticed that his ewes had had a lot more problems with mastitis, pneumonia and foot problems than usual, which he now knows are some of the clinical signs seen in sheep with MV.

He said that it took five years of hard work to eradicate MV from their flocks and become MV accredited again, and estimated that the disease cost them £250,000 in lost production, blood testing, AI and embryo transfer, artificial lamb rearing and reduced income in pedigree ram sales.

"Dealing with a full blown MV outbreak has without question given me a renewed respect for achieving full MV Accredited status and I would urge fellow scheme members not to treat that very privelaged status lightly" said Mr Brown. 

MV is of particular interest to the Borders monitor farmers Robert, Lesley and son Stuart Mitchell, who run the 460 hectare Whitriggs farm, as the disease has recently been diagnosed on their flock of 1,000 Lleyns.

Stuart Mitchell explained: “Following a previous monitor farm meeting where we looked at our lamb performance, we decided to do some routine blood tests on our ewes, as we felt our flock performance was not as good as it should be, such as scan percentage, number  of lambs weaned and growth rates. Visually there didn’t seem to be much wrong with the ewes. ”

He added: “When the results came back positive for MV we were really shocked. We didn’t know much about the disease and didn’t know what the affect would be for our sheep enterprise.

“We have now tested all of our gimmers and 45% have tested positive for MV, so we are working with our vet to decide how we can move forward and eradicate this disease from our flock.”

The Mitchells are unsure how MV managed to infect the flock at Whitriggs as they have run a closed flock since 2001 and only buy in MV accredited rams. They are pragmatic about things though and realise that the key thing to focus on now is how to remove it from their flock.

Lesley Mitchell said: “We are really grateful for the help and support we have received from our vet  Andrew Robinson, and to the local farmers at today’s meeting, who have come up with lots of suggestions as to how we can manage our sheep enterprise whilst we work towards eradicating MV.”

She added: “We are fortunate that due to being part of the monitor farm programme, we blood tested our sheep, otherwise MV would have remained undetected in our flock and we would have continued to see production losses for some time to come. Now we know what we are dealing with we can do something about it.”

Facilitator for the Borders Monitor Farm, Stephen Young, confirmed at this week’s meeting that the monitor farm project has agreed to cover the costs of initial screening 20 local flocks for MV to try and discover how big an issue it is in the area.

The results will be shared at a future monitor farm meeting but the details of the flocks which are tested will remain anonymous. Farmers wishing to take up this offer are asked to contact their vet or the VI centre at St Boswells in confidence.

Whitriggs farm is one of nine monitor farms established in Scotland as part of a joint initiative by Quality Meat Scotland (QMS) and AHDB Cereals & Oilseeds with funding from the Scottish Government. The aim of the monitor farm programme is to help improve the productivity, profitability and sustainability of Scottish farm businesses.

For more information about the monitor farm programme visit www.monitorfarms.co.uk