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Ovine Pulmonary Adenocarcinoma, better known as OPA or Jaagsiekte, is an important cause of mortality in NI sheep flocks.
Speaking at last week’s Future-proofing your sheep enterprise conference, Co Down vet Patrick Grant outlined how ultrasound scanning remains the only accurate method of diagnosing OPA in sheep.
OPA is a viral lung cancer and does not cause an immune response, therefore blood tests and tissue sampling are ineffective at diagnosing it.
As there is no known treatment, animals with OPA are destined to die either directly from the disease, or from a secondary infection such as pneumonia.
According to Grant, OPA affects all breeds of sheep, not just hill animals, and animals in good condition are just as likely to have a tumour as those that are thin.
The alternative is these positive animals will eventually lose flesh and die with zero cull value
Scanning costs £2/ewe, or £200 for a 100-ewe flock. According to Grant, if four ewes are culled at £50/head immediately after a positive scanning, this covers the cost of scanning the whole flock.
The alternative is these positive animals will eventually lose flesh and die with zero cull value, said Grant.
At the event, just 6% of farmers said that they have scanned for OPA, 42% have plans to scan in the near future, and 32% indicated that they do not believe it is a problem on their farm.
Meanwhile at CAFRE, after several years with too many unexplained deaths, sheep technologist Dr Eileen McCloskey said that the decision was taken to scan both hill and lowland flocks for the disease.
Results showed OPA affected animals had reduced to 5.3% across the flocks
At the first scan, 8.7% of all ewes on CAFRE flocks had signs of OPA and were culled. Sheep were re-scanned six months later, with 9.2% affected.
A second major cull followed before a third scan was carried out prior to lambing this spring.
Results showed OPA affected animals had reduced to 5.3% across the flocks.
Culling has worked, and a fourth scan last week saw just 1.6% of all sheep affected.
The plan is now to scan the flock every 12 months, with breeding rams checked after purchase and post-breeding.
Rotational grazing delivers big
Also speaking at last weeks’ sheep conference, Co Tyrone farmer Isaac Crilly outlined how rotational grazing has benefitted his 400-ewe flock.
With a stocking rate of 14 ewes/ha and 185% of lambs weaned per ewe on a 70ac (28.3ha) grassland farm, grazing demand is extremely high. To highlight the benefits of rotational grazing, ewes and lambs graze in two groups of 150 on two 4.8ha land blocks.
The first block is divided in eight 0.6ha divisions, with the second block set up in four 1.2ha paddocks.
Lambs are finished at 17kg to 20kg carcase weight to ease grazing pressure
Grass growth across the two blocks is measured weekly and in 2018, the farm grew 13t DM/ha compared with the average NI sheep farm of 4.8t DM/ha. This year grass growth averaged close to 16t DM/ha, but utilisation has been much lower.
Lambs are finished at 17kg to 20kg carcase weight to ease grazing pressure.
“We don’t send free kilos to the factory. We sell 540kg/ha of lamb with 20% of animals U-grading and 78% R-grading in conformation,” said Isaac.
Focus on carcase specification
Getting lambs to the correct carcase specification remains a key area where sheep farmers can make big efficiency gains, Michaela Tener from Dunbia told farmers at last weeks’ sheep conference.
It costs four times more to produce 1kg of fat cover, compared with 1kg of lean meat
The average lamb carcase weight in NI is 21.6kg, with 40% of animals falling outside of market specification.
Tener outlined that 50% of NI lambs are sold through retail outlets, which require carcases weighing 17kg to 19kg at fat class two and three.
“It costs four times more to produce 1kg of fat cover, compared with 1kg of lean meat.
"Therefore, producing lambs above the carcase limit comes at a significant cost to the farmer, yet they do not get paid for this additional weight,” said Tener.
Tener also highlighted the importance of good handling to prevent carcase bruising just prior to slaughter, restricting injection sites to the neck to prevent abscesses developing in the loin cuts and also presenting clean lambs for slaughter during autumn and winter months.
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