Jaagsiekte or Ovine Pulmonary Adenocarcinoma (OPA), is becoming an increasing problem in all sheep breeds and crosses, and while there is not cure or vaccine for the disease, flock masters can now control the disease to some extent with ultrasound scanning.

Research carried out by several flocks in the Clyde Wind Farm project showed that while scanning for tumours in the lung caused by this viral disease, was not a perfect test, it is useful in reducing the long-term prevalence in flocks.

"I think we can finally do something to reduce the risk of OPA in sheep flocks, but it requires a complete flock approach," said Dr Chris Cousens, who has been looking into the causes of the disease and ultimately a vaccine or cure for this debilitating disease that can cause severe breathlessness, loss of condition and eventually death.

Speaking at last week's Scotsheep event at Kings Arms Farm, Ballantrae, she said: "The test is not perfect but it looks pretty good as scanning will never detect microscopic OPA or virus infection prior to tumour development."

However, Dr Cousens stressed that producers looking to reduce the incidence of the disease should scan all sheep over a year old and not just new stock rams, or rams to be sold as is the case on a growing number of flocks in recent years.

"It is not sensible to scan only tups when the biggest cause of OPA in a flock is probably ewe to lamb transmission of the virus."

In the project, all sheep over a year old were scanned twice a year and while some positives appeared soon after scanning (probably less than 1:5000), the results showed that the tumour in these instances developed rapidly from tiny to big enough to cause clinical signs of disease. However, the proportion of OPA positive sheep in flocks was between 0% and 5% and in almost all cases reduced in the second year. In the one situation the number of positive OPA sheep increased from five out of 450 in year one, to six out of 450 in the second year.

To further reduce the incidence of OPA, Dr Cousens pointed out that more flocks with the disease have to scan on a regular basis, which would not only enable flock masters to cull sheep when they still have a value, but also reduce the risk of the disease spreading.

What still remains unknown however, is how many years will it take to get to no positive OPA sheep in a flock and how many years after that does a flock have to scan to remain clear of the disease.