A Welsh sheep farm has reduced prevalence of the highly infectious disease ovine pulmonary adenocarcinoma (OPA) in its flock to 4 per cent from a one time high of 11.6 per cent by culling in combination with ultrasound scanning and new biosecurity measures.

OPA, a viral infection which results is tumours within the lungs, was diagnosed in the flock at Court Farm, Llanthony, near Abergavenny, in 2021 after several ewes showed clinical signs: they were thin, breathing heavily and had excessive nasal discharge.

The flock’s scanning rate had also reduced by 30 per cent to 140 per cent.

A post mortem on one of the animals identified extensive OPA lesions – the first time the disease had been diagnosed in the flock.

Bryony Gittins, who farms in partnership with her father, Colin Passmore, embarked on a Farming Connect focus site project using thoracic ultrasound scanning to establish the true incidence of OPA within the flock and to limit the risk of the disease being re-introduced after culling affected ewes.

In February 2021, ultrasound scanning of all ewes over two years old detected a 3.7 per cent incidence among 545 animals – in August 457 were scanned and the incidence level had increased to 11.6 per cent.

Mrs Gittins has since adopted a scan and cull policy – any animals that test positive are culled or, if they are pregnant, they are marked and lamb separately from the main flock, and are sold with the progeny as soon as the lambs have hit slaughter weights of 41-45kg.

As a result, scanning in February 2022 showed that the infection rate had fallen to 4 per cent – 23 were identified with OPA and of those four had clinical signs and 19 lesions on their lungs.

Scanning is an ongoing cost – approximately £2 a ewe – but it needs to be done, says Mrs Gittins.

Action has also been taken to improve flock biosecurity, including improving boundary fences to prevent nose-to-nose contact between her sheep and those grazing neighbouring land.

Pregnant ewes are kept at grass a month later than normal, to the end of January, because there is greater likelihood of the disease spreading when animals are housed; housing also increases the risk of ewes with underlying OPA succumbing to secondary illnesses such as pneumonia due to the stress of switching from a grass-based diet in an open air environment to being inside and eating silage.

Body condition scoring is being done more frequently and thin sheep culled because even without an OPA diagnosis a thin sheep will be less productive, she points out.

Her next step is to invest in software to record lambs born from ewes with OPA as the disease will pass to lambs because they are in close proximity to the ewe.

Those lambs won’t be retained as replacements, but will be sold fat or as stores.

“Lambs don’t show clinical signs of OPA until they are two years or older and they don’t pass it on so there is no issue with selling them as stores,’’ says Mrs Gittins.

She is working towards a position where the infection rate is stable and to rebuilding numbers after taking the initial financial hit.

Another option is to cull the entire flock and to restock with ‘clean’ animals but Mrs Gittins says there is no guarantee that those wouldn’t be infected with OPA or other diseases.

Many flocks may be harbouring OPA without owners knowing it therefore the scale of OPA in the UK sheep flock could be much higher than is being reported.

“It is likely that there are greater numbers of flocks with iceberg diseases that farmers are just not aware of because without looking for these and without careful monitoring you just don’t know they are there,’’ says Mrs Gittins.

“Building a good relationship with the farm vet can help with diagnosis.’’

Working with Farming Connect on this project had been a very valuable opportunity, she says.

“It has enabled me to gather knowledge and the information to make my decisions going forward on the future of this flock at Court Farm.’’