Method for OPA control showing good initial results

Reduction

Results up to now had shown that, generally, flocks were seeing a reduction in OPA positive results year-on-year since they had started the process.

Dr Cousens said: “Ultrasound screening is never going to be able to detect the very smallest OPA tumours, but it can detect the disease before an animal begins to display any clinical signs.

“This means those animals can be identified for culling at a saleable value, but it also goes some way to eliminating the welfare issue of keeping sheep, although not intentionally, on-farm with an incurable disease.

“The overall trend is good but we have noted that it does take time and persistence, particularly in flocks which had a high number of positive cases to start with [more than 5 per cent positive tests at first scan], to reduce prevalence.

“We also do not know how long it is going to take to get all flocks to an overall negative screening result.”

With the popularity and uptake of the scan and cull approach said to be increasing, Dr Cousens said it was also key to understand what ultrasound results meant.

She highlighted that a single negative scanning result on an animal could not serve as a guarantee that OPA was not present, only that ‘no lesions were found’ as a result of the scan.

Lessons had also been learnt about the scanning procedure during the research, as well as OPA itself.

Although previously thought of as a slow developing disease, very regular scanning as part of the research [every three weeks] on one group of sheep had shown it to develop more rapidly, from less than 1cm in diameter to up to 7cm over three months.