8 March 2022
Ovine pulmonary adenocarcinoma (OPA) was diagnosed in the flock at Court Farm, Llanthony, near Abergavenny, in 2021, after several ewes showed clinical signs; the group were thin, were breathing heavily, and had excessive nasal discharge. There had also been a 30% reduction in the flock’s pregnancy scanning rate, from 170% to 140%.
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% incidence among 545 animals. The following August, 457 were scanned, and the incidence level had increased to 11.6%.
Mrs Gittins has adopted a scan-and cull-policy: any animals that test positive are culled or, if they are pregnant, they are marked, kept separately, with their lambs, from the main flock, and are sold with the progeny as soon as the lambs have hit slaughter weights of 41-45kg.
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 investing in improvements to boundary fences to prevent nose-to-nose contact between her sheep and those grazing neighbouring land.
Pregnant ewes are also being 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.
“When the sheep are outdoors, they have a lot more space, and they are not sharing a water tank because they have access to a stream,’’ Mrs Gittins explains.
She had been bolusing the flock once a year for trace elements and offering powdered minerals, but they are now bolused twice a year, to remove any risk of OPA being spread through the feeding of minerals.
Body condition scoring is also being carried out more frequently, and thin sheep culled – because even without an OPA diagnosis, a thin sheep will be less productive, she points out.
Mrs Gittins’ 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 re-building 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.
The business would also take a financial hit from culling the entire flock – at a cull value of £90 a ewe, the sale of 550 animals would raise £49,500, compared to the £93,500 cost of buying in replacements at £170 a head. However, some of the £44,000 deficit would be recouped; Mrs Gittins calculates that increasing the scanning rate from 145% to 170% would produce 138 additional lambs, and generate an income of around £9,660 a year.
By retaining the flock, there is also an annual lung scanning cost, and a higher culling rate, making the sheep worth less. But Mrs Gittins says she is not willing to take the risk of buying in unless she can be sure that she won’t find herself in a similar position with a new flock.
Restocking is an option for the future, though: “I will always keep it at the back of my mind, if there is a flock dispersal where I could get a similar breed from a single farm, I might think ‘let’s go with this’.’’
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.’’
OPA is a viral infection which results in tumours within the lungs.
Vicky Fisher, of Abergavenny-based Farm First Vets, who has worked with Mrs Gittins on the Farming Connect project, says it is spread through nasal secretions:
“Clinical signs, if you see them, are generally weight loss and general respiratory signs, so it can be coughing and increased labouring when they are trying to breathe - you may see them tummy breathing.
“Because this virus causes tumours in the cells that produce the fluid within the lungs, then in about half of cases, you will see copious amounts of fluid coming out of the nose or out of the mouth.’’
The nasal excretions contain the virus and infect the rest of the flock. The disease manifests in older animals, but they pick it up when they are much younger - the symptoms just take a while to be evident. The disease is terminal, and there is no treatment. Infected animals will either die from the tumours, or because lung damage results in a bacterial infection, causing septicaemia and killing the animal.
Ms Fisher says controlling the disease can be difficult:
“Unfortunately tests are fairly limited, so at the moment, we can only do lung scanning where we scan a portion of the lungs on both sides – which is where we most commonly find tumours.’’
There are new tests in development in the UK, but these are not yet commercially available.
Farming Connect is delivered by Menter a Busnes and Lantra Wales, and funded by the Welsh Government and the European Agricultural Fund for Rural Development.